diff --git a/htdocs/admin/usergroup.php b/htdocs/admin/usergroup.php
index 15939c806c25e..e5d93114c7cf9 100644
--- a/htdocs/admin/usergroup.php
+++ b/htdocs/admin/usergroup.php
@@ -28,12 +28,9 @@
  *		\ingroup    core
  *		\brief      Page to setup usergroup module
  */
+namespace Dolibarr\User;
 
-// Load Dolibarr environment
-require '../main.inc.php';
-require_once DOL_DOCUMENT_ROOT.'/core/lib/usergroups.lib.php';
-require_once DOL_DOCUMENT_ROOT.'/core/lib/admin.lib.php';
-require_once DOL_DOCUMENT_ROOT.'/core/class/extrafields.class.php';
+use Dolibarr\{ExtraFields};
 
 /**
  * @var Conf $conf
diff --git a/htdocs/core/boxes/box_lastlogin.php b/htdocs/core/boxes/box_lastlogin.php
index 6ec1d99c03216..09f62f5c8cd73 100644
--- a/htdocs/core/boxes/box_lastlogin.php
+++ b/htdocs/core/boxes/box_lastlogin.php
@@ -23,9 +23,9 @@
  *  \ingroup    core
  *  \brief      Module to show box of last user logins
  */
+namespace Dolibarr;
 
-include_once DOL_DOCUMENT_ROOT.'/core/boxes/modules_boxes.php';
-
+use Dolibarr\ModeleBoxes;
 /**
  *  Class to manage the box of last login
  */
diff --git a/htdocs/core/boxes/modules_boxes.php b/htdocs/core/boxes/modules_boxes.php
index 5ebf55004ada8..ebd4cd8443511 100644
--- a/htdocs/core/boxes/modules_boxes.php
+++ b/htdocs/core/boxes/modules_boxes.php
@@ -25,7 +25,7 @@
  *		\ingroup    core
  *		\brief      File containing the parent class of boxes
  */
-
+namespace Dolibarr;
 
 /**
  * Class ModeleBoxes
diff --git a/htdocs/core/class/Autoloader.php b/htdocs/core/class/Autoloader.php
new file mode 100644
index 0000000000000..9d3470b7da6db
--- /dev/null
+++ b/htdocs/core/class/Autoloader.php
@@ -0,0 +1,52 @@
+<?php
+
+namespace Dolibarr;
+
+class Autoloader {
+
+	public static function register(): void {
+		spl_autoload_register([self::class, 'autoload']);
+	}
+
+	public static function autoload($class): void {
+		// Check that namespace is in Dolibarr
+		if (!str_starts_with($class, 'Dolibarr\\')) {
+			return;
+		}
+
+		$relativeClass = substr($class, strlen('Dolibarr\\'));
+		$relativeClassPath = str_replace('\\', DIRECTORY_SEPARATOR, $relativeClass);
+
+        $classNamespaceParts = explode('\\', $class);
+        $moduleName = (count($classNamespaceParts) < 3) ? '' : $classNamespaceParts[count($classNamespaceParts) - 2];
+
+		$baseDirectories = [
+			realpath(__DIR__) . DIRECTORY_SEPARATOR,
+			realpath(__DIR__) . '/../' . strtolower($moduleName) . DIRECTORY_SEPARATOR,
+			realpath(__DIR__ . '/../../custom/') . strtolower($moduleName) . DIRECTORY_SEPARATOR,
+		];
+
+		// We need to check all the possible class file names, until they all follow the correct syntax
+		$filePatterns = [
+			strtolower(basename($relativeClassPath)) . '.class.php',
+			basename($relativeClassPath) . '.class.php',
+			strtolower(basename($relativeClassPath)) . '.interface.php',
+			basename($relativeClassPath) . '.interface.php',
+			strtolower(dirname($relativeClassPath)) . '.' . strtolower(basename($relativeClassPath)) . '.class.php',
+			basename($relativeClassPath) . '.php'
+		];
+
+		foreach ($baseDirectories as $baseDir) {
+			foreach ($filePatterns as $pattern) {
+				$possiblePath = $baseDir . $pattern;
+				if (file_exists($possiblePath)) {
+					require_once $possiblePath;
+					return;
+				}
+			}
+		}
+	}
+
+}
+
+Autoloader::register();
diff --git a/htdocs/core/class/commonincoterm.class.php b/htdocs/core/class/commonincoterm.class.php
index 35aad5285706d..49817d6f6f4df 100644
--- a/htdocs/core/class/commonincoterm.class.php
+++ b/htdocs/core/class/commonincoterm.class.php
@@ -21,6 +21,7 @@
  *       \ingroup    core
  *       \brief      File of the superclass of object classes that support incoterm (customer and supplier)
  */
+namespace Dolibarr;
 
 
 /**
diff --git a/htdocs/core/class/commonobject.class.php b/htdocs/core/class/commonobject.class.php
index 07db3b1340955..452235a3b0702 100644
--- a/htdocs/core/class/commonobject.class.php
+++ b/htdocs/core/class/commonobject.class.php
@@ -39,8 +39,9 @@
  *	\ingroup    core
  *	\brief      File of parent class of all other business classes (invoices, contracts, proposals, orders, ...)
  */
+namespace Dolibarr;
 
-require_once DOL_DOCUMENT_ROOT.'/core/class/doldeprecationhandler.class.php';
+//require_once DOL_DOCUMENT_ROOT.'/core/class/doldeprecationhandler.class.php';
 
 /**
  *	Parent class of all other business classes (invoices, contracts, proposals, orders, ...)
diff --git a/htdocs/core/class/commonobjectline.class.php b/htdocs/core/class/commonobjectline.class.php
index 173cd852be1fc..6a112b0482fe8 100644
--- a/htdocs/core/class/commonobjectline.class.php
+++ b/htdocs/core/class/commonobjectline.class.php
@@ -23,7 +23,7 @@
  *  \ingroup    core
  *  \brief      File of the superclass of classes of lines of business objects (invoice, contract, proposal, orders, etc. ...)
  */
-
+namespace Dolibarr;
 
 /**
  *  Parent class for class inheritance lines of business objects
diff --git a/htdocs/core/class/commonpeople.class.php b/htdocs/core/class/commonpeople.class.php
index a4e9096b06732..074d166ca52dc 100644
--- a/htdocs/core/class/commonpeople.class.php
+++ b/htdocs/core/class/commonpeople.class.php
@@ -21,7 +21,7 @@
  *       \ingroup    core
  *       \brief      File of the superclass of object classes that support people
  */
-
+namespace Dolibarr;
 
 /**
  *      Support class for third parties, contacts, members, users or resources
diff --git a/htdocs/core/class/commonsocialnetworks.class.php b/htdocs/core/class/commonsocialnetworks.class.php
index 0c7a61a9c5b66..5a9ff756a4e3d 100644
--- a/htdocs/core/class/commonsocialnetworks.class.php
+++ b/htdocs/core/class/commonsocialnetworks.class.php
@@ -21,7 +21,7 @@
  *       \ingroup    core
  *       \brief      File of the superclass of object classes that support socialnetworks
  */
-
+namespace Dolibarr;
 
 /**
  *      Superclass for social networks
diff --git a/htdocs/core/class/conf.class.php b/htdocs/core/class/conf.class.php
index 2a78aded5ac8a..806b222776456 100644
--- a/htdocs/core/class/conf.class.php
+++ b/htdocs/core/class/conf.class.php
@@ -28,6 +28,9 @@
  *  \brief      	File of class to manage storage of current setup
  *  				Config is stored into file conf.php
  */
+namespace Dolibarr;
+
+use stdClass;
 
 /**
  *  Class to stock current configuration
diff --git a/htdocs/core/class/defaultvalues.class.php b/htdocs/core/class/defaultvalues.class.php
index c92697a4a9fa3..5cae726e6fd60 100644
--- a/htdocs/core/class/defaultvalues.class.php
+++ b/htdocs/core/class/defaultvalues.class.php
@@ -22,11 +22,7 @@
  * \file        htdocs/core/class/defaultvalues.class.php
  * \brief       This file is a CRUD class file for DefaultValues (Create/Read/Update/Delete)
  */
-
-// Put here all includes required by your class file
-require_once DOL_DOCUMENT_ROOT.'/core/class/commonobject.class.php';
-//require_once DOL_DOCUMENT_ROOT . '/societe/class/societe.class.php';
-//require_once DOL_DOCUMENT_ROOT . '/product/class/product.class.php';
+namespace Dolibarr;
 
 /**
  * Class for MyObject
diff --git a/htdocs/core/class/doldeprecationhandler.class.php b/htdocs/core/class/doldeprecationhandler.class.php
index bb68b683481c9..5c796ebd36ae3 100644
--- a/htdocs/core/class/doldeprecationhandler.class.php
+++ b/htdocs/core/class/doldeprecationhandler.class.php
@@ -20,6 +20,7 @@
  * @ingroup       core
  * @brief         trait for handling deprecated properties and methods
  */
+namespace Dolibarr;
 
 /**
  * Class for handling deprecated properties and methods
diff --git a/htdocs/core/class/extrafields.class.php b/htdocs/core/class/extrafields.class.php
index aebd001f0266f..0f6a14d864774 100644
--- a/htdocs/core/class/extrafields.class.php
+++ b/htdocs/core/class/extrafields.class.php
@@ -34,7 +34,7 @@
  *	\ingroup    core
  *	\brief      File of class to manage extra fields
  */
-
+namespace Dolibarr;
 
 /**
  *	Class to manage standard extra fields
diff --git a/htdocs/core/class/hookmanager.class.php b/htdocs/core/class/hookmanager.class.php
index bfc13a8d33726..162526e60a6ba 100644
--- a/htdocs/core/class/hookmanager.class.php
+++ b/htdocs/core/class/hookmanager.class.php
@@ -24,7 +24,7 @@
  *	\ingroup    core
  *	\brief      File of class to manage hooks
  */
-
+namespace Dolibarr;
 
 /**
  *	Class to manage hooks
diff --git a/htdocs/core/class/html.form.class.php b/htdocs/core/class/html.form.class.php
index 77c8eb3e13787..4309286909a9a 100644
--- a/htdocs/core/class/html.form.class.php
+++ b/htdocs/core/class/html.form.class.php
@@ -47,7 +47,10 @@
  * \brief      File of class with all html predefined components
  */
 
+namespace Dolibarr\HTML;
 
+use stdClass;
+use Dolibarr\ModeleBoxes;
 /**
  * Class to manage generation of HTML components
  * Only common components must be here.
diff --git a/htdocs/core/class/html.formaccounting.class.php b/htdocs/core/class/html.formaccounting.class.php
index fae07b24a6b91..9873ef6a202f3 100644
--- a/htdocs/core/class/html.formaccounting.class.php
+++ b/htdocs/core/class/html.formaccounting.class.php
@@ -26,9 +26,8 @@
  *  \ingroup    Accountancy (Double entries)
  *	\brief      File of class with all html predefined components
  */
-require_once DOL_DOCUMENT_ROOT.'/core/class/html.form.class.php';
-
 
+namespace Dolibarr\HTML;
 /**
  *	Class to manage generation of HTML components for accounting management
  */
diff --git a/htdocs/core/class/html.formactions.class.php b/htdocs/core/class/html.formactions.class.php
index c8238d4770c35..486c41c11099d 100644
--- a/htdocs/core/class/html.formactions.class.php
+++ b/htdocs/core/class/html.formactions.class.php
@@ -26,6 +26,7 @@
  */
 
 
+namespace Dolibarr\HTML;
 /**
  *      Class to manage building of HTML components
  */
diff --git a/htdocs/core/class/html.formadmin.class.php b/htdocs/core/class/html.formadmin.class.php
index 65b4cea3a88c0..9bdf3cd71fb88 100644
--- a/htdocs/core/class/html.formadmin.class.php
+++ b/htdocs/core/class/html.formadmin.class.php
@@ -26,6 +26,7 @@
  */
 
 
+namespace Dolibarr\HTML;
 /**
  *      Class to generate html code for admin pages
  */
diff --git a/htdocs/core/class/html.formai.class.php b/htdocs/core/class/html.formai.class.php
index f317c2d1be2a9..864fd5a691d46 100644
--- a/htdocs/core/class/html.formai.class.php
+++ b/htdocs/core/class/html.formai.class.php
@@ -29,9 +29,8 @@
  *       \ingroup    core
  *       \brief      Fichier de la class permettant la generation du formulaire html d'envoi de mail unitaire
  */
-require_once DOL_DOCUMENT_ROOT.'/core/class/html.form.class.php';
-
 
+namespace Dolibarr\HTML;
 /**
  *      Class permettant la generation du formulaire html d'envoi de mail unitaire
  *      Usage: $formail = new FormAI($db)
diff --git a/htdocs/core/class/html.formbank.class.php b/htdocs/core/class/html.formbank.class.php
index 9d50a0bb60b97..530ec1f4466e8 100644
--- a/htdocs/core/class/html.formbank.class.php
+++ b/htdocs/core/class/html.formbank.class.php
@@ -23,9 +23,7 @@
  *	\brief      File of class with all html predefined components
  */
 
-include_once DOL_DOCUMENT_ROOT.'/compta/bank/class/account.class.php';
-
-
+namespace Dolibarr\HTML;
 /**
  *	Class to manage generation of HTML components for bank module
  */
diff --git a/htdocs/core/class/html.formbarcode.class.php b/htdocs/core/class/html.formbarcode.class.php
index d113aa44d6cbe..97c0fa5906e21 100644
--- a/htdocs/core/class/html.formbarcode.class.php
+++ b/htdocs/core/class/html.formbarcode.class.php
@@ -24,7 +24,7 @@
  *      \brief      Fichier de la class des functions predefinie de composants html
  */
 
-
+namespace Dolibarr\HTML;
 /**
  *      Class to manage barcode HTML
  */
diff --git a/htdocs/core/class/html.formcategory.class.php b/htdocs/core/class/html.formcategory.class.php
index 4a91fbc99f7e3..6f998c644fe8c 100644
--- a/htdocs/core/class/html.formcategory.class.php
+++ b/htdocs/core/class/html.formcategory.class.php
@@ -23,10 +23,7 @@
  *	\brief		File of class to build HTML component for category filtering
  */
 
-require_once DOL_DOCUMENT_ROOT.'/core/class/html.form.class.php';
-require_once DOL_DOCUMENT_ROOT.'/categories/class/categorie.class.php';
-
-
+namespace Dolibarr\HTML;
 /**
  *	Class to manage forms for categories
  */
diff --git a/htdocs/core/class/html.formcompany.class.php b/htdocs/core/class/html.formcompany.class.php
index cf42ba4b738ae..eb8288ce1c02f 100644
--- a/htdocs/core/class/html.formcompany.class.php
+++ b/htdocs/core/class/html.formcompany.class.php
@@ -27,14 +27,12 @@
  *	\brief      File of class to build HTML component for third parties management
  */
 
-
+namespace Dolibarr\HTML;
 /**
  *	Class to build HTML component for third parties management
  *	Only common components are here.
  */
 
-require_once DOL_DOCUMENT_ROOT . '/core/class/html.form.class.php';
-
 
 /**
  * Class of forms component to manage companies
diff --git a/htdocs/core/class/html.formcontract.class.php b/htdocs/core/class/html.formcontract.class.php
index 11eca55e4b6ae..b370f269b0afe 100644
--- a/htdocs/core/class/html.formcontract.class.php
+++ b/htdocs/core/class/html.formcontract.class.php
@@ -23,6 +23,7 @@
  * \brief      File of class with all html predefined components
  */
 
+namespace Dolibarr\HTML;
 /**
  *	Class to manage generation of HTML components for contract module
  */
diff --git a/htdocs/core/class/html.formcron.class.php b/htdocs/core/class/html.formcron.class.php
index fde4fd8e3f3a2..af4de02f8d5ee 100644
--- a/htdocs/core/class/html.formcron.class.php
+++ b/htdocs/core/class/html.formcron.class.php
@@ -23,7 +23,7 @@
  *      \brief      Fichier de la class des functions predefinie de composants html cron
  */
 
-
+namespace Dolibarr\HTML;
 /**
  *      Class to manage building of HTML components
  */
diff --git a/htdocs/core/class/html.formexpensereport.class.php b/htdocs/core/class/html.formexpensereport.class.php
index 4e64a9356c17e..96856c3e114c4 100644
--- a/htdocs/core/class/html.formexpensereport.class.php
+++ b/htdocs/core/class/html.formexpensereport.class.php
@@ -22,6 +22,7 @@
  * \brief      File of class with all html predefined components
  */
 
+namespace Dolibarr\HTML;
 /**
  *	Class to manage generation of HTML components for contract module
  */
diff --git a/htdocs/core/class/html.formfile.class.php b/htdocs/core/class/html.formfile.class.php
index 30b233204ff01..589bea6a09ccf 100644
--- a/htdocs/core/class/html.formfile.class.php
+++ b/htdocs/core/class/html.formfile.class.php
@@ -31,7 +31,7 @@
  *	\brief      File of class to offer components to list and upload files
  */
 
-
+namespace Dolibarr\HTML;
 /**
  *	Class to offer components to list and upload files
  */
diff --git a/htdocs/core/class/html.formfiscalyear.class.php b/htdocs/core/class/html.formfiscalyear.class.php
index 9f49aa16f4124..93e3c34cfe429 100644
--- a/htdocs/core/class/html.formfiscalyear.class.php
+++ b/htdocs/core/class/html.formfiscalyear.class.php
@@ -20,8 +20,8 @@
  *  \ingroup    Accountancy (Double entries)
  *	\brief      File of class with all html predefined components
  */
-require_once DOL_DOCUMENT_ROOT.'/core/class/html.form.class.php';
 
+namespace Dolibarr\HTML;
 /**
  *	Class to manage generation of HTML components for accounting management
  */
diff --git a/htdocs/core/class/html.formintervention.class.php b/htdocs/core/class/html.formintervention.class.php
index 484ff337738eb..de2c7a447ca01 100644
--- a/htdocs/core/class/html.formintervention.class.php
+++ b/htdocs/core/class/html.formintervention.class.php
@@ -23,6 +23,7 @@
  * \brief      File of class with all html predefined components
  */
 
+namespace Dolibarr\HTML;
 /**
  *	Class to manage generation of HTML components for contract module
  */
diff --git a/htdocs/core/class/html.formldap.class.php b/htdocs/core/class/html.formldap.class.php
index d96cbcca56850..bf5e78b3fa82e 100644
--- a/htdocs/core/class/html.formldap.class.php
+++ b/htdocs/core/class/html.formldap.class.php
@@ -21,8 +21,8 @@
  *       \ingroup    core
  *       \brief      File of class with ldap html predefined components
  */
-require_once DOL_DOCUMENT_ROOT.'/core/class/html.form.class.php';
 
+namespace Dolibarr\HTML;
 /**
  *      Class to manage generation of HTML components for ldap module
  */
diff --git a/htdocs/core/class/html.formmail.class.php b/htdocs/core/class/html.formmail.class.php
index 52d6b58655548..d45a5f436a54c 100644
--- a/htdocs/core/class/html.formmail.class.php
+++ b/htdocs/core/class/html.formmail.class.php
@@ -29,9 +29,8 @@
  *       \ingroup    core
  *       \brief      Fichier de la class permettant la generation du formulaire html d'envoi de mail unitaire
  */
-require_once DOL_DOCUMENT_ROOT.'/core/class/html.form.class.php';
-
 
+namespace Dolibarr\HTML;
 /**
  *      Class permettant la generation du formulaire html d'envoi de mail unitaire
  *      Usage: $formail = new FormMail($db)
diff --git a/htdocs/core/class/html.formmailing.class.php b/htdocs/core/class/html.formmailing.class.php
index ed2152956f196..b8478d2f50960 100644
--- a/htdocs/core/class/html.formmailing.class.php
+++ b/htdocs/core/class/html.formmailing.class.php
@@ -21,8 +21,8 @@
  *  \ingroup    core
  *	\brief      File of predefined functions for HTML forms for mailing module
  */
-require_once DOL_DOCUMENT_ROOT.'/core/class/html.form.class.php';
 
+namespace Dolibarr\HTML;
 /**
  *  Class to offer components to list and upload files
  */
diff --git a/htdocs/core/class/html.formmargin.class.php b/htdocs/core/class/html.formmargin.class.php
index a18d28b9f32de..4de4f0c9b7594 100644
--- a/htdocs/core/class/html.formmargin.class.php
+++ b/htdocs/core/class/html.formmargin.class.php
@@ -23,7 +23,7 @@
  *	\brief      Fichier de la class des functions predefinie de composants html autre
  */
 
-
+namespace Dolibarr\HTML;
 /**
  *	Class permettant la generation de composants html autre
  *	Only common components are here.
diff --git a/htdocs/core/class/html.formorder.class.php b/htdocs/core/class/html.formorder.class.php
index b7d51181310d6..f7138cd1736e1 100644
--- a/htdocs/core/class/html.formorder.class.php
+++ b/htdocs/core/class/html.formorder.class.php
@@ -23,9 +23,7 @@
  *	\brief      File of predefined functions for HTML forms for order module
  */
 
-require_once DOL_DOCUMENT_ROOT.'/core/class/html.form.class.php';
-require_once DOL_DOCUMENT_ROOT.'/commande/class/commande.class.php';
-
+namespace Dolibarr\HTML;
 /**
  *	Class to manage HTML output components for orders
  *	Before adding component here, check they are not into common part Form.class.php
diff --git a/htdocs/core/class/html.formother.class.php b/htdocs/core/class/html.formother.class.php
index 09a9daa59940a..7f5183e0b8eab 100644
--- a/htdocs/core/class/html.formother.class.php
+++ b/htdocs/core/class/html.formother.class.php
@@ -33,7 +33,9 @@
  *	\brief      Fichier de la class des functions predefinie de composants html autre
  */
 
+namespace Dolibarr\HTML;
 
+use Dolibarr\{InfoBox, ModeleBoxes};
 /**
  *	Class permettant la generation de composants html autre
  *	Only common components are here.
@@ -459,7 +461,6 @@ public function select_categories($type, $selected = 0, $htmlname = 'search_cate
 
 		// Enhance with select2
 		if ($conf->use_javascript_ajax) {
-			include_once DOL_DOCUMENT_ROOT.'/core/lib/ajax.lib.php';
 			$comboenhancement = ajax_combobox('select_categ_'.$htmlname);
 			$moreforfilter .= $comboenhancement;
 		}
@@ -1225,7 +1226,6 @@ public static function getBoxesArea($user, $areacode)
 	{
 		global $conf, $langs, $db;
 
-		include_once DOL_DOCUMENT_ROOT.'/core/class/infobox.class.php';
 		// From include
 		'
 		@phan-var-force ModeleBoxes[] $boxactivated
diff --git a/htdocs/core/class/html.formprojet.class.php b/htdocs/core/class/html.formprojet.class.php
index 2534c04a58c0e..4a63511f0cc1f 100644
--- a/htdocs/core/class/html.formprojet.class.php
+++ b/htdocs/core/class/html.formprojet.class.php
@@ -26,8 +26,7 @@
  *      \brief      Class file for html component project
  */
 
-require_once DOL_DOCUMENT_ROOT.'/core/class/html.form.class.php';
-
+namespace Dolibarr\HTML;
 /**
  *      Class to manage building of HTML components
  */
diff --git a/htdocs/core/class/html.formpropal.class.php b/htdocs/core/class/html.formpropal.class.php
index 3142b991aaeac..4cc4ba3e01134 100644
--- a/htdocs/core/class/html.formpropal.class.php
+++ b/htdocs/core/class/html.formpropal.class.php
@@ -22,7 +22,7 @@
  *	\brief      File of class with all html predefined components
  */
 
-
+namespace Dolibarr\HTML;
 /**
  *	Class to manage generation of HTML components for proposal management
  */
diff --git a/htdocs/core/class/html.formsetup.class.php b/htdocs/core/class/html.formsetup.class.php
index b3addf7f7db2b..b7075b16372c9 100644
--- a/htdocs/core/class/html.formsetup.class.php
+++ b/htdocs/core/class/html.formsetup.class.php
@@ -16,6 +16,7 @@
  * along with this program. If not, see <https://www.gnu.org/licenses/>.
  */
 
+namespace Dolibarr\HTML;
 /**
  * This class help you create setup render
  */
diff --git a/htdocs/core/class/html.formsms.class.php b/htdocs/core/class/html.formsms.class.php
index cf82ca3c81c5f..33233080ed6df 100644
--- a/htdocs/core/class/html.formsms.class.php
+++ b/htdocs/core/class/html.formsms.class.php
@@ -23,9 +23,8 @@
  *       \ingroup    core
  *       \brief      Fichier de la class permettant la generation du formulaire html d'envoi de mail unitaire
  */
-require_once DOL_DOCUMENT_ROOT.'/core/class/html.form.class.php';
-
 
+namespace Dolibarr\HTML;
 /**
  *      Class permettant la generation du formulaire d'envoi de Sms
  *      Usage: $formsms = new FormSms($db)
diff --git a/htdocs/core/class/html.formsocialcontrib.class.php b/htdocs/core/class/html.formsocialcontrib.class.php
index 06d0f4ae8d3a7..fb48ec30a5fe9 100644
--- a/htdocs/core/class/html.formsocialcontrib.class.php
+++ b/htdocs/core/class/html.formsocialcontrib.class.php
@@ -22,7 +22,7 @@
  *	\brief      File of class with all html predefined components
  */
 
-
+namespace Dolibarr\HTML;
 /**
  *	Class to manage generation of HTML components for social contributions management
  */
diff --git a/htdocs/core/class/html.formticket.class.php b/htdocs/core/class/html.formticket.class.php
index 5ba1465f7b44f..2cf02a7ef4d1e 100644
--- a/htdocs/core/class/html.formticket.class.php
+++ b/htdocs/core/class/html.formticket.class.php
@@ -28,14 +28,8 @@
  *    \brief      File of class to generate the form for creating a new ticket.
  */
 
-require_once DOL_DOCUMENT_ROOT . '/core/class/html.form.class.php';
-require_once DOL_DOCUMENT_ROOT . '/core/class/html.formmail.class.php';
-require_once DOL_DOCUMENT_ROOT . '/core/class/html.formprojet.class.php';
-
-if (!class_exists('FormCompany')) {
-	include DOL_DOCUMENT_ROOT.'/core/class/html.formcompany.class.php';
-}
 
+namespace Dolibarr\HTML;
 /**
  * Class to generate the form for creating a new ticket.
  * Usage: 	$formticket = new FormTicket($db)
diff --git a/htdocs/core/class/html.formwebsite.class.php b/htdocs/core/class/html.formwebsite.class.php
index afea3d81e3c09..b3e684ee59cb4 100644
--- a/htdocs/core/class/html.formwebsite.class.php
+++ b/htdocs/core/class/html.formwebsite.class.php
@@ -22,7 +22,7 @@
  *	\brief      File of class to manage component html for module website
  */
 
-
+namespace Dolibarr\HTML;
 /**
  *	Class to manage component html for module website
  */
diff --git a/htdocs/core/class/infobox.class.php b/htdocs/core/class/infobox.class.php
index 68340e873d28d..49243b7d79ccc 100644
--- a/htdocs/core/class/infobox.class.php
+++ b/htdocs/core/class/infobox.class.php
@@ -24,6 +24,7 @@
  *	\brief      File of class to manage widget boxes
  */
 
+namespace Dolibarr;
 /**
  *	Class to manage boxes on pages. This is an utility class (all is static)
  */
diff --git a/htdocs/core/class/translate.class.php b/htdocs/core/class/translate.class.php
index 8f1d46ed5ca3e..834380d7b758e 100644
--- a/htdocs/core/class/translate.class.php
+++ b/htdocs/core/class/translate.class.php
@@ -24,7 +24,7 @@
  *      \ingroup    core
  *		\brief      File for Translate class
  */
-
+namespace Dolibarr;
 
 /**
  *		Class to manage translations
diff --git a/htdocs/core/db/Database.interface.php b/htdocs/core/db/Database.interface.php
index 046f850472223..d515ee259a27d 100644
--- a/htdocs/core/db/Database.interface.php
+++ b/htdocs/core/db/Database.interface.php
@@ -21,7 +21,7 @@
  * You should have received a copy of the GNU General Public License
  * along with this program. If not, see <https://www.gnu.org/licenses/>.
  */
-
+namespace Dolibarr\DB;
 /**
  *    Class to manage Dolibarr database access for an SQL database
  */
diff --git a/htdocs/core/db/DoliDB.class.php b/htdocs/core/db/DoliDB.class.php
index 63847079776e5..e59e567eb6ab9 100644
--- a/htdocs/core/db/DoliDB.class.php
+++ b/htdocs/core/db/DoliDB.class.php
@@ -23,9 +23,7 @@
  * \file 		htdocs/core/db/DoliDB.class.php
  * \brief 		Class file to manage Dolibarr database access
  */
-
-require_once DOL_DOCUMENT_ROOT.'/core/db/Database.interface.php';
-
+namespace Dolibarr\DB;
 
 /**
  * Class to manage Dolibarr database access
diff --git a/htdocs/core/db/mysqli.class.php b/htdocs/core/db/mysqli.class.php
index 160805761bc39..9142dfec03ca1 100644
--- a/htdocs/core/db/mysqli.class.php
+++ b/htdocs/core/db/mysqli.class.php
@@ -269,7 +269,7 @@ public function connect($host, $login, $passwd, $name, $port = 0)
 			if (strpos($host, 'ssl://') === 0) {
 				$tmp = new mysqliDoli($host, $login, $passwd, $name, $port);
 			} else {
-				$tmp = new mysqli($host, $login, $passwd, $name, $port);
+				$tmp = new \mysqli($host, $login, $passwd, $name, $port);
 			}
 		} catch (Exception $e) {
 			dol_syslog(get_class($this)."::connect failed", LOG_DEBUG);
diff --git a/htdocs/core/lib/functions.lib.php b/htdocs/core/lib/functions.lib.php
index d1ea43af5d121..03bf6fb09e46f 100644
--- a/htdocs/core/lib/functions.lib.php
+++ b/htdocs/core/lib/functions.lib.php
@@ -425,7 +425,7 @@ function getDoliDBInstance($type, $host, $user, $pass, $name, $port)
 {
 	require_once DOL_DOCUMENT_ROOT."/core/db/".$type.'.class.php';
 
-	$class = 'DoliDB'.ucfirst($type);
+	$class = 'Dolibarr\\DB\\DoliDB'.ucfirst($type);
 	$db = new $class($type, $host, $user, $pass, $name, $port);
 	return $db;
 }
@@ -452,7 +452,6 @@ function getEntity($element, $shared = 1, $currentobject = null)
 	global $conf, $mc, $hookmanager, $object, $action, $db;
 
 	if (!is_object($hookmanager)) {
-		include_once DOL_DOCUMENT_ROOT.'/core/class/hookmanager.class.php';
 		$hookmanager = new HookManager($db);
 	}
 
@@ -2898,7 +2897,6 @@ function dol_get_fiche_head($links = array(), $active = '', $title = '', $notab
 		$out .= '">'."\n";
 	}
 	if (!empty($dragdropfile)) {
-		include_once DOL_DOCUMENT_ROOT.'/core/lib/files.lib.php';
 		$out .= dragAndDropFileUpload("dragDropAreaTabBar");
 	}
 	$parameters = array('tabname' => $active, 'out' => $out);
@@ -3122,7 +3120,6 @@ function dol_banner_tab($object, $paramid, $morehtml = '', $shownav = 1, $fieldi
 						// Conversion du PDF en image png si fichier png non existent
 						if (!file_exists($fileimage) || (filemtime($fileimage) < filemtime($filepdf))) {
 							if (!getDolGlobalString('MAIN_DISABLE_PDF_THUMBS')) {		// If you experience trouble with pdf thumb generation and imagick, you can disable here.
-								include_once DOL_DOCUMENT_ROOT.'/core/lib/files.lib.php';
 								$ret = dol_convert_file($filepdf, 'png', $fileimage, '0'); // Convert first page of PDF into a file _preview.png
 								if ($ret < 0) {
 									$error++;
@@ -3870,7 +3867,6 @@ function dol_now($mode = 'auto')
 	if ($mode == 'gmt') {
 		$ret = time(); // Time for now at greenwich.
 	} elseif ($mode == 'tzserver') {		// Time for now with PHP server timezone added
-		require_once DOL_DOCUMENT_ROOT.'/core/lib/date.lib.php';
 		$tzsecond = getServerTimeZoneInt('now'); // Contains tz+dayling saving time
 		$ret = (int) (dol_now('gmt') + ($tzsecond * 3600));
 		//} elseif ($mode == 'tzref') {// Time for now with parent company timezone is added
@@ -4080,7 +4076,6 @@ function getArrayOfSocialNetworks()
 
 	$socialnetworks = array();
 	// Enable caching of array
-	require_once DOL_DOCUMENT_ROOT.'/core/lib/memory.lib.php';
 	$cachekey = 'socialnetworks_' . $conf->entity;
 	$dataretrieved = dol_getcache($cachekey);
 	if (!is_null($dataretrieved)) {
@@ -4703,7 +4698,6 @@ function dolGetCountryCodeFromIp($ip)
 		$datafile = getDolGlobalString('GEOIPMAXMIND_COUNTRY_DATAFILE');
 		//$ip='24.24.24.24';
 		//$datafile='/usr/share/GeoIP/GeoIP.dat';    Note that this must be downloaded datafile (not same than datafile provided with ubuntu packages)
-		include_once DOL_DOCUMENT_ROOT.'/core/class/dolgeoip.class.php';
 		$geoip = new DolGeoIP('country', $datafile);
 		//print 'ip='.$ip.' databaseType='.$geoip->gi->databaseType." GEOIP_CITY_EDITION_REV1=".GEOIP_CITY_EDITION_REV1."\n";
 		$countrycode = $geoip->getCountryCodeFromIP($ip);
@@ -4730,7 +4724,6 @@ function dol_user_country()
 		$datafile = getDolGlobalString('GEOIPMAXMIND_COUNTRY_DATAFILE');
 		//$ip='24.24.24.24';
 		//$datafile='E:\Mes Sites\Web\Admin1\awstats\maxmind\GeoIP.dat';
-		include_once DOL_DOCUMENT_ROOT.'/core/class/dolgeoip.class.php';
 		$geoip = new DolGeoIP('country', $datafile);
 		$countrycode = $geoip->getCountryCodeFromIP($ip);
 		$ret = $countrycode;
@@ -5995,8 +5988,6 @@ function img_credit_card($brand, $morecss = null)
  */
 function img_mime($file, $titlealt = '', $morecss = '')
 {
-	require_once DOL_DOCUMENT_ROOT.'/core/lib/files.lib.php';
-
 	$mimetype = dol_mimetype($file, '', 1);
 	$mimeimg = dol_mimetype($file, '', 2);
 	$mimefa = dol_mimetype($file, '', 4);
@@ -6128,7 +6119,6 @@ function dol_print_error($db = null, $error = '', $errors = null)
 
 	// If error occurs before the $lang object was loaded
 	if (!$langs) {
-		require_once DOL_DOCUMENT_ROOT.'/core/class/translate.class.php';
 		$langs = new Translate('', $conf);
 		$langs->load("main");
 	}
@@ -7139,8 +7129,6 @@ function price2num($amount, $rounding = '', $option = 0)
  */
 function showDimensionInBestUnit($dimension, $unit, $type, $outputlangs, $round = -1, $forceunitoutput = 'no', $use_short_label = 0)
 {
-	require_once DOL_DOCUMENT_ROOT.'/core/lib/product.lib.php';
-
 	if (($forceunitoutput == 'no' && $dimension < 1 / 10000 && $unit < 90) || (is_numeric($forceunitoutput) && $forceunitoutput == -6)) {
 		$dimension *= 1000000;
 		$unit -= 6;
@@ -7524,8 +7512,6 @@ function get_product_vat_for_country($idprod, $thirdpartytouse, $idprodfournpric
 {
 	global $db, $mysoc;
 
-	require_once DOL_DOCUMENT_ROOT.'/product/class/product.class.php';
-
 	$ret = 0;
 	$found = 0;
 
@@ -7619,10 +7605,6 @@ function get_product_localtax_for_country($idprod, $local, $thirdpartytouse)
 {
 	global $db, $mysoc;
 
-	if (!class_exists('Product')) {
-		require_once DOL_DOCUMENT_ROOT.'/product/class/product.class.php';
-	}
-
 	$ret = 0;
 	$found = 0;
 
@@ -7692,8 +7674,6 @@ function get_default_tva(Societe $thirdparty_seller, Societe $thirdparty_buyer,
 {
 	global $conf, $db;
 
-	require_once DOL_DOCUMENT_ROOT.'/core/lib/company.lib.php';
-
 	// Note: possible values for tva_assuj are 0/1 or franchise/reel
 	$seller_use_vat = ((is_numeric($thirdparty_seller->tva_assuj) && !$thirdparty_seller->tva_assuj) || (!is_numeric($thirdparty_seller->tva_assuj) && $thirdparty_seller->tva_assuj == 'franchise')) ? 0 : 1;
 
@@ -7711,7 +7691,6 @@ function get_default_tva(Societe $thirdparty_seller, Societe $thirdparty_buyer,
 		if ($seller_in_cee && $buyer_in_cee) {
 			$isacompany = $thirdparty_buyer->isACompany();
 			if ($isacompany && getDolGlobalString('MAIN_USE_VAT_COMPANIES_IN_EEC_WITH_INVALID_VAT_ID_ARE_INDIVIDUAL')) {
-				require_once DOL_DOCUMENT_ROOT.'/core/lib/functions2.lib.php';
 				if (!isValidVATID($thirdparty_buyer)) {
 					$isacompany = 0;
 				}
@@ -7780,7 +7759,6 @@ function get_default_tva(Societe $thirdparty_seller, Societe $thirdparty_buyer,
 	if (($seller_in_cee && $buyer_in_cee)) {
 		$isacompany = $thirdparty_buyer->isACompany();
 		if ($isacompany && getDolGlobalString('MAIN_USE_VAT_COMPANIES_IN_EEC_WITH_INVALID_VAT_ID_ARE_INDIVIDUAL')) {
-			require_once DOL_DOCUMENT_ROOT.'/core/lib/functions2.lib.php';
 			if (!isValidVATID($thirdparty_buyer)) {
 				$isacompany = 0;
 			}
@@ -7827,16 +7805,10 @@ function get_default_npr(Societe $thirdparty_seller, Societe $thirdparty_buyer,
 	global $db;
 
 	if ($idprodfournprice > 0) {
-		if (!class_exists('ProductFournisseur')) {
-			require_once DOL_DOCUMENT_ROOT.'/fourn/class/fournisseur.product.class.php';
-		}
 		$prodprice = new ProductFournisseur($db);
 		$prodprice->fetch_product_fournisseur_price($idprodfournprice);
 		return $prodprice->fourn_tva_npr;
 	} elseif ($idprod > 0) {
-		if (!class_exists('Product')) {
-			require_once DOL_DOCUMENT_ROOT.'/product/class/product.class.php';
-		}
 		$prod = new Product($db);
 		$prod->fetch($idprod);
 		return $prod->tva_npr;
@@ -9489,7 +9461,6 @@ function getCommonSubstitutionArray($outputlangs, $onlykey = 0, $exclude = null,
 				$paymenturl = '';
 			} else {
 				// Set the online payment url link into __ONLINE_PAYMENT_URL__ key
-				require_once DOL_DOCUMENT_ROOT.'/core/lib/payments.lib.php';
 				$outputlangs->loadLangs(array('paypal', 'other'));
 
 				$amounttouse = 0;
@@ -9523,7 +9494,6 @@ function getCommonSubstitutionArray($outputlangs, $onlykey = 0, $exclude = null,
 
 				// Show structured communication
 				if (getDolGlobalString('INVOICE_PAYMENT_ENABLE_STRUCTURED_COMMUNICATION') && $object->element == 'facture') {
-					include_once DOL_DOCUMENT_ROOT.'/core/lib/functions_be.lib.php';
 					$substitutionarray['__PAYMENT_STRUCTURED_COMMUNICATION__'] = dolBECalculateStructuredCommunication($object->ref, $object->type);
 				}
 
@@ -9561,7 +9531,6 @@ function getCommonSubstitutionArray($outputlangs, $onlykey = 0, $exclude = null,
 				if (is_object($object) && $object->element == 'propal') {
 					'@phan-var-force Propal $object';
 					$substitutionarray['__URL_PROPOSAL__'] = DOL_MAIN_URL_ROOT."/comm/propal/card.php?id=".$object->id;
-					require_once DOL_DOCUMENT_ROOT.'/core/lib/signature.lib.php';
 					$substitutionarray['__ONLINE_SIGN_URL__'] = getOnlineSignatureUrl(0, 'proposal', $object->ref, 1, $object);
 				}
 				if (is_object($object) && $object->element == 'commande') {
@@ -9575,13 +9544,11 @@ function getCommonSubstitutionArray($outputlangs, $onlykey = 0, $exclude = null,
 				if (is_object($object) && $object->element == 'contrat') {
 					'@phan-var-force Contrat $object';
 					$substitutionarray['__URL_CONTRACT__'] = DOL_MAIN_URL_ROOT."/contrat/card.php?id=".$object->id;
-					require_once DOL_DOCUMENT_ROOT.'/core/lib/signature.lib.php';
 					$substitutionarray['__ONLINE_SIGN_URL__'] = getOnlineSignatureUrl(0, 'contract', $object->ref, 1, $object);
 				}
 				if (is_object($object) && $object->element == 'fichinter') {
 					'@phan-var-force Fichinter $object';
 					$substitutionarray['__URL_FICHINTER__'] = DOL_MAIN_URL_ROOT."/fichinter/card.php?id=".$object->id;
-					require_once DOL_DOCUMENT_ROOT.'/core/lib/signature.lib.php';
 					$substitutionarray['__ONLINE_SIGN_FICHINTER_URL__'] = getOnlineSignatureUrl(0, 'fichinter', $object->ref, 1, $object);
 				}
 				if (is_object($object) && $object->element == 'supplier_proposal') {
@@ -9609,7 +9576,6 @@ function getCommonSubstitutionArray($outputlangs, $onlykey = 0, $exclude = null,
 	}
 	if ((empty($exclude) || !in_array('objectamount', $exclude)) && (empty($include) || in_array('objectamount', $include))) {
 		'@phan-var-force Facture|FactureRec $object';
-		include_once DOL_DOCUMENT_ROOT.'/core/lib/functionsnumtoword.lib.php';
 
 		$substitutionarray['__DATE_YMD__']          = is_object($object) ? (isset($object->date) ? dol_print_date($object->date, 'day', false, $outputlangs) : null) : '';
 		$substitutionarray['__DATE_DUE_YMD__']      = is_object($object) ? (isset($object->date_lim_reglement) ? dol_print_date($object->date_lim_reglement, 'day', false, $outputlangs) : null) : '';
@@ -9683,8 +9649,6 @@ function getCommonSubstitutionArray($outputlangs, $onlykey = 0, $exclude = null,
 
 
 	if ((empty($exclude) || !in_array('date', $exclude)) && (empty($include) || in_array('date', $include))) {
-		include_once DOL_DOCUMENT_ROOT.'/core/lib/date.lib.php';
-
 		$now = dol_now();
 
 		$tmp = dol_getdate($now, true);
@@ -9940,8 +9904,6 @@ function complete_substitutions_array(&$substitutionarray, $outputlangs, $object
 {
 	global $conf, $user;
 
-	require_once DOL_DOCUMENT_ROOT.'/core/lib/files.lib.php';
-
 	// Note: substitution key for each extrafields, using key __EXTRA_XXX__ is already available into the getCommonSubstitutionArray used to build the substitution array.
 
 	// Check if there is external substitution to do, requested by plugins
@@ -13738,7 +13700,6 @@ function getElementProperties($elementType)
 
 	// Add  hook
 	if (!is_object($hookmanager)) {
-		include_once DOL_DOCUMENT_ROOT.'/core/class/hookmanager.class.php';
 		$hookmanager = new HookManager($db);
 	}
 	$hookmanager->initHooks(array('elementproperties'));
@@ -14559,8 +14520,6 @@ function show_actions_messaging($conf, $langs, $db, $filterobj, $objcon = null,
 
 	global $param, $massactionbutton;
 
-	require_once DOL_DOCUMENT_ROOT . '/comm/action/class/actioncomm.class.php';
-
 	// Check parameters
 	if (!is_object($filterobj) && !is_object($objcon)) {
 		dol_print_error(null, 'BadParameter');
@@ -14876,11 +14835,6 @@ function show_actions_messaging($conf, $langs, $db, $filterobj, $objcon = null,
 	if (isModEnabled('agenda') || (isModEnabled('mailing') && !empty($objcon->email))) {
 		$delay_warning = getDolGlobalInt('MAIN_DELAY_ACTIONS_TODO') * 24 * 60 * 60;
 
-		require_once DOL_DOCUMENT_ROOT.'/comm/action/class/actioncomm.class.php';
-		include_once DOL_DOCUMENT_ROOT.'/core/lib/functions2.lib.php';
-		require_once DOL_DOCUMENT_ROOT.'/core/class/html.formactions.class.php';
-		require_once DOL_DOCUMENT_ROOT.'/contact/class/contact.class.php';
-
 		$formactions = new FormActions($db);
 
 		$actionstatic = new ActionComm($db);
@@ -14977,7 +14931,6 @@ function show_actions_messaging($conf, $langs, $db, $filterobj, $objcon = null,
 			$out .= getTitleFieldOfList($tmp);
 		}
 
-		require_once DOL_DOCUMENT_ROOT.'/comm/action/class/cactioncomm.class.php';
 		$caction = new CActionComm($db);
 		$arraylist = $caction->liste_array(1, 'code', '', (!getDolGlobalString('AGENDA_USE_EVENT_TYPE') ? 1 : 0), '', 1);
 
@@ -15360,7 +15313,6 @@ function recordNotFound($message = '', $printheader = 1, $printfooter = 1, $show
 	global $action, $object;
 
 	if (!is_object($langs)) {
-		include_once DOL_DOCUMENT_ROOT.'/core/class/translate.class.php';
 		$langs = new Translate('', $conf);
 		$langs->setDefaultLang();
 	}
@@ -15386,7 +15338,6 @@ function recordNotFound($message = '', $printheader = 1, $printfooter = 1, $show
 
 	if (empty($showonlymessage)) {
 		if (empty($hookmanager)) {
-			include_once DOL_DOCUMENT_ROOT.'/core/class/hookmanager.class.php';
 			$hookmanager = new HookManager($db);
 			// Initialize a technical object to manage hooks of page. Note that conf->hooks_modules contains an array of hook context
 			$hookmanager->initHooks(array('main'));
diff --git a/htdocs/core/tpl/login.tpl.php b/htdocs/core/tpl/login.tpl.php
index ef2f44d06304c..7c936eec79aae 100644
--- a/htdocs/core/tpl/login.tpl.php
+++ b/htdocs/core/tpl/login.tpl.php
@@ -23,6 +23,8 @@
 // Caller can also set 	$morelogincontent = array(['options']=>array('js'=>..., 'table'=>...);
 // $titletruedolibarrversion must be defined
 
+require_once __DIR__ . "/../lib/functions.lib.php";
+
 if (!defined('NOBROWSERNOTIF')) {
 	define('NOBROWSERNOTIF', 1);
 }
diff --git a/htdocs/index.php b/htdocs/index.php
index b8e6d089292b9..6fe739cf4555b 100644
--- a/htdocs/index.php
+++ b/htdocs/index.php
@@ -30,8 +30,12 @@
 
 define('CSRFCHECK_WITH_TOKEN', 1); // We force need to use a token to login when making a POST
 
+require_once __DIR__.'/core/class/Autoloader.php';
 require 'main.inc.php';
-require_once DOL_DOCUMENT_ROOT.'/core/class/html.formother.class.php';
+
+use Dolibarr\HTML\FormOther;
+use Dolibarr\InfoBox;
+use Dolibarr\HTML\Form;
 
 /**
  * @var Conf $conf
@@ -71,7 +75,6 @@
 	exit;
 }
 if (GETPOST('addbox')) {	// Add box (when submit is done from a form when ajax disabled)
-	require_once DOL_DOCUMENT_ROOT.'/core/class/infobox.class.php';
 	$zone = GETPOSTINT('areacode');
 	$userid = GETPOSTINT('userid');
 	$boxorder = GETPOST('boxorder', 'aZ09');
diff --git a/htdocs/main.inc.php b/htdocs/main.inc.php
index 5c06842b25d61..be517ce9e3d62 100644
--- a/htdocs/main.inc.php
+++ b/htdocs/main.inc.php
@@ -38,6 +38,8 @@
  *	\ingroup	core
  *	\brief      File that defines environment for Dolibarr GUI pages only (file not required by scripts)
  */
+require_once __DIR__ . "/core/class/Autoloader.php";
+require_once __DIR__ . "/core/lib/functions.lib.php";
 
 //@ini_set('memory_limit', '128M');	// This may be useless if memory is hard limited by your PHP
 
diff --git a/htdocs/master.inc.php b/htdocs/master.inc.php
index d7e9a5b0505f2..8b5e1398b1633 100644
--- a/htdocs/master.inc.php
+++ b/htdocs/master.inc.php
@@ -32,12 +32,10 @@
  *  \brief      File that defines environment for all Dolibarr process (pages or scripts)
  * 				This script reads the conf file, init $lang, $db and and empty $user
  */
+namespace Dolibarr;
 
 // Include the conf.php and functions.lib.php and security.lib.php. This defined the constants like DOL_DOCUMENT_ROOT, DOL_DATA_ROOT, DOL_URL_ROOT...
 // This file may have been already required by main.inc.php. But may not by scripts. So, here the require_once must be kept.
-require_once 'filefunc.inc.php';
-require_once DOL_DOCUMENT_ROOT.'/core/class/conf.class.php';
-require_once DOL_DOCUMENT_ROOT.'/core/class/hookmanager.class.php';
 /**
  * @var Translate $langs
  *
diff --git a/htdocs/multicurrency/class/currencyrate.class.php b/htdocs/multicurrency/class/currencyrate.class.php
index dbeed1d2749ba..30c50ad091a1d 100644
--- a/htdocs/multicurrency/class/currencyrate.class.php
+++ b/htdocs/multicurrency/class/currencyrate.class.php
@@ -27,8 +27,7 @@
  * \ingroup multicurrency
  * \brief   This file is a CRUD class file (Create/Read/Update/Delete) for currencyrate
  */
-
-require_once DOL_DOCUMENT_ROOT.'/core/class/commonobjectline.class.php';
+namespace Dolibarr;
 
 /**
  * Class CurrencyRate
diff --git a/htdocs/multicurrency/class/multicurrency.class.php b/htdocs/multicurrency/class/multicurrency.class.php
index 2523134ed3653..a8a55c3a0f2cf 100644
--- a/htdocs/multicurrency/class/multicurrency.class.php
+++ b/htdocs/multicurrency/class/multicurrency.class.php
@@ -26,9 +26,7 @@
  * \ingroup multicurrency
  * \brief   This file is a CRUD class file (Create/Read/Update/Delete) for multicurrency
  */
-
-require_once DOL_DOCUMENT_ROOT.'/core/class/commonobject.class.php';
-require_once DOL_DOCUMENT_ROOT.'/multicurrency/class/currencyrate.class.php';
+namespace Dolibarr\MultiCurrency;
 
 /**
  * Class Currency
diff --git a/htdocs/product/class/html.formproduct.class.php b/htdocs/product/class/html.formproduct.class.php
index d3aeeb8d17dc9..92dc98af8f3a6 100644
--- a/htdocs/product/class/html.formproduct.class.php
+++ b/htdocs/product/class/html.formproduct.class.php
@@ -23,8 +23,7 @@
  *	\brief      File for class with methods for building product related HTML components
  */
 
-require_once DOL_DOCUMENT_ROOT.'/product/stock/class/entrepot.class.php';
-
+namespace Dolibarr\HTML;
 /**
  *	Class with static methods for building HTML components related to products
  *	Only components common to products and services must be here.
diff --git a/htdocs/societe/class/societe.class.php b/htdocs/societe/class/societe.class.php
index 5ff1c35496aa0..f94698bcad129 100644
--- a/htdocs/societe/class/societe.class.php
+++ b/htdocs/societe/class/societe.class.php
@@ -42,13 +42,10 @@
  *	\ingroup    societe
  *	\brief      File for third party class
  */
-require_once DOL_DOCUMENT_ROOT.'/core/class/commonobject.class.php';
-require_once DOL_DOCUMENT_ROOT.'/core/class/commonincoterm.class.php';
-require_once DOL_DOCUMENT_ROOT.'/core/class/commonsocialnetworks.class.php';
-require_once DOL_DOCUMENT_ROOT.'/core/class/commonpeople.class.php';
-require_once DOL_DOCUMENT_ROOT.'/core/lib/company.lib.php';
-require_once DOL_DOCUMENT_ROOT.'/multicurrency/class/multicurrency.class.php';
+namespace Dolibarr\ThirdParty;
 
+use Dolibarr\{CommonObject, CommonPeople, CommonIncoterm, CommonSocialNetworks, Conf};
+use Dolibarr\MultiCurrency\MultiCurrency;
 
 /**
  *	Class to manage third parties objects (customers, suppliers, prospects...)
diff --git a/htdocs/societe/index.php b/htdocs/societe/index.php
index 11332a7febd55..168dc4d0e6468 100644
--- a/htdocs/societe/index.php
+++ b/htdocs/societe/index.php
@@ -27,12 +27,12 @@
  *  \ingroup    societe
  *  \brief      Home page for third parties area
  */
+namespace Dolibarr;
 
+use Dolibarr\HTML\FormOther;
+use Dolibarr\HookManager;
 // Load Dolibarr environment
 require '../main.inc.php';
-require_once DOL_DOCUMENT_ROOT.'/societe/class/societe.class.php';
-require_once DOL_DOCUMENT_ROOT.'/contact/class/contact.class.php';
-require_once DOL_DOCUMENT_ROOT.'/core/class/html.formother.class.php';
 
 /**
  * @var Conf $conf
diff --git a/htdocs/user/class/user.class.php b/htdocs/user/class/user.class.php
index ba728ebc94ca2..7c8e2573adb34 100644
--- a/htdocs/user/class/user.class.php
+++ b/htdocs/user/class/user.class.php
@@ -36,12 +36,10 @@
  *	\brief      File of class to manage users
  *  \ingroup	core
  */
+namespace Dolibarr\User;
 
-require_once DOL_DOCUMENT_ROOT.'/core/lib/security.lib.php';
-require_once DOL_DOCUMENT_ROOT.'/core/class/commonobject.class.php';
-require_once DOL_DOCUMENT_ROOT.'/user/class/usergroup.class.php';
-require_once DOL_DOCUMENT_ROOT.'/core/class/commonpeople.class.php';
-
+use Dolibarr\{CommonObject, CommonPeople, DefaultValues};
+use stdClass;
 
 /**
  *	Class to manage Dolibarr users
@@ -820,7 +818,6 @@ public function loadDefaultValues()
 
 		if (getDolGlobalString('MAIN_ENABLE_DEFAULT_VALUES')) {
 			// Load user->default_values for user. TODO Save this in memcached ?
-			require_once DOL_DOCUMENT_ROOT.'/core/class/defaultvalues.class.php';
 
 			$defaultValues = new DefaultValues($this->db);
 			$result = $defaultValues->fetchAll('', '', 0, 0, '(t.user_id:in:0,'.$this->id.') AND (entity:in:'.(isset($this->entity) ? $this->entity : $conf->entity).','.$conf->entity.')');	// User 0 (all) + me (if defined)