diff --git a/Cargo.toml b/Cargo.toml
index 6a11287..4c713c8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -24,21 +24,23 @@ include = [
 ]
 
 [features]
+default = ["std"]
+std = ["regex?/std", "unicode-normalization?/std"]
 # Includes the full canonical text of each license
 text = []
 # Allows analysis of text to determine if it might be an SPDX license text
-detection = ["regex", "unicode-normalization"]
+detection = ["std", "regex", "unicode-normalization"]
 # Allows de/serialization of a spdx::detection::Store for quicker loading
-detection-cache = ["detection", "zstd"]
+detection-cache = ["std", "detection", "zstd"]
 # Inlines a cache into this crate, which contains all of the licenses from the
 # SPDX crate that the crate version was packaged with
-detection-inline-cache = ["detection-cache"]
+detection-inline-cache = ["std", "detection-cache"]
 # Performs license detection in parallel within the same text
-detection-parallel = ["detection", "rayon"]
+detection-parallel = ["std", "detection", "rayon"]
 
 [dependencies]
 rayon = { version = "1.11", optional = true }
-regex = { version = "1.12", optional = true }
+regex = { version = "1.12", optional = true, default-features = false, features = ["perf", "unicode"] }
 # In most cases expressions are quite small so we can avoid heap allocations
 smallvec = "1.15"
 unicode-normalization = { version = "0.1", optional = true }
diff --git a/src/error.rs b/src/error.rs
index acfb77c..2be80e8 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -1,4 +1,5 @@
-use std::{error::Error, fmt};
+use alloc::string::String;
+use core::{error::Error, fmt};
 
 /// An error related to parsing of an SPDX license expression
 /// or identifier
@@ -8,7 +9,7 @@ pub struct ParseError {
     pub original: String,
     /// The range of characters in the original string that result
     /// in this error
-    pub span: std::ops::Range<usize>,
+    pub span: core::ops::Range<usize>,
     /// The specific reason for the error
     pub reason: Reason,
 }
diff --git a/src/expression.rs b/src/expression.rs
index 8dfd267..a9254a1 100644
--- a/src/expression.rs
+++ b/src/expression.rs
@@ -4,9 +4,11 @@ mod minimize;
 mod parser;
 
 use crate::{LicenseReq, error::ParseError};
+use alloc::string::String;
+use alloc::vec::Vec;
+use core::fmt;
 pub use minimize::MinimizeError;
 use smallvec::SmallVec;
-use std::fmt;
 
 /// A license requirement inside an SPDX license expression
 ///
@@ -16,7 +18,7 @@ pub struct ExpressionReq {
     /// The license requirement
     pub req: LicenseReq,
     /// The span in the original license expression string containing the requirement
-    pub span: std::ops::Range<u32>,
+    pub span: core::ops::Range<u32>,
 }
 
 impl PartialEq for ExpressionReq {
@@ -238,7 +240,7 @@ impl fmt::Display for Expression {
     }
 }
 
-impl std::str::FromStr for Expression {
+impl core::str::FromStr for Expression {
     type Err = ParseError;
     fn from_str(s: &str) -> Result<Self, Self::Err> {
         Self::parse(s)
diff --git a/src/expression/minimize.rs b/src/expression/minimize.rs
index 8e53652..78e6a9d 100644
--- a/src/expression/minimize.rs
+++ b/src/expression/minimize.rs
@@ -1,6 +1,7 @@
 use super::Expression;
 use crate::{LicenseReq, Licensee};
-use std::fmt;
+use alloc::vec::Vec;
+use core::fmt;
 
 /// Errors that can occur when trying to minimize the requirements for an [`Expression`]
 #[derive(Debug, PartialEq, Eq)]
@@ -25,7 +26,7 @@ impl fmt::Display for MinimizeError {
     }
 }
 
-impl std::error::Error for MinimizeError {
+impl core::error::Error for MinimizeError {
     fn description(&self) -> &str {
         match self {
             Self::TooManyRequirements(_) => "too many requirements in license expression",
diff --git a/src/expression/parser.rs b/src/expression/parser.rs
index b4385f3..e29f63a 100644
--- a/src/expression/parser.rs
+++ b/src/expression/parser.rs
@@ -4,6 +4,9 @@ use crate::{
     expression::{ExprNode, Expression, ExpressionReq, Operator},
     lexer::{Lexer, Token},
 };
+use alloc::borrow::ToOwned;
+use alloc::boxed::Box;
+use alloc::string::String;
 use smallvec::SmallVec;
 
 impl Expression {
@@ -163,7 +166,7 @@ impl Expression {
 
         struct OpAndSpan {
             op: Op,
-            span: std::ops::Range<usize>,
+            span: core::ops::Range<usize>,
         }
 
         let lexer = Lexer::new_mode(original, mode);
@@ -184,7 +187,7 @@ impl Expression {
             Ok(())
         };
 
-        let make_err_for_token = |last_token: Option<Token<'_>>, span: std::ops::Range<usize>| {
+        let make_err_for_token = |last_token: Option<Token<'_>>, span: core::ops::Range<usize>| {
             let expected: &[&str] = match last_token {
                 None | Some(Token::And | Token::Or | Token::OpenParen) => &["<license>", "("],
                 Some(Token::CloseParen) => &["AND", "OR"],
diff --git a/src/lexer.rs b/src/lexer.rs
index fd45cde..025787b 100644
--- a/src/lexer.rs
+++ b/src/lexer.rs
@@ -2,6 +2,7 @@ use crate::{
     ExceptionId, LicenseId,
     error::{ParseError, Reason},
 };
+use alloc::borrow::ToOwned;
 
 /// Parsing configuration for SPDX expression
 #[derive(Default, Copy, Clone)]
@@ -106,9 +107,9 @@ pub enum Token<'a> {
     Or,
 }
 
-impl std::fmt::Display for Token<'_> {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        std::fmt::Debug::fmt(self, f)
+impl core::fmt::Display for Token<'_> {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        core::fmt::Debug::fmt(self, f)
     }
 }
 
@@ -244,7 +245,7 @@ pub struct LexerToken<'a> {
     /// The token that was lexed
     pub token: Token<'a>,
     /// The range of the token characters in the original license expression
-    pub span: std::ops::Range<usize>,
+    pub span: core::ops::Range<usize>,
 }
 
 impl<'a> Iterator for Lexer<'a> {
diff --git a/src/lib.rs b/src/lib.rs
index f0e56b4..1188be7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,6 +1,9 @@
 #![cfg_attr(docsrs, feature(doc_cfg))]
 #![deny(missing_docs)]
 #![doc = include_str!("../README.md")]
+#![cfg_attr(not(feature = "std"), no_std)]
+
+extern crate alloc;
 
 /// Error types
 pub mod error;
@@ -21,14 +24,16 @@ pub mod detection;
 #[allow(missing_docs)]
 pub mod text;
 
+use alloc::boxed::Box;
+use alloc::string::String;
+use core::{
+    cmp::{self, Ordering},
+    fmt,
+};
 pub use error::ParseError;
 pub use expression::Expression;
 pub use lexer::ParseMode;
 pub use licensee::Licensee;
-use std::{
-    cmp::{self, Ordering},
-    fmt,
-};
 
 /// Flags that can apply to licenses and/or license exceptions
 pub mod flags {
@@ -87,7 +92,7 @@ impl Eq for LicenseId {}
 
 impl Ord for LicenseId {
     #[inline]
-    fn cmp(&self, o: &Self) -> Ordering {
+    fn cmp(&self, o: &Self) -> core::cmp::Ordering {
         self.l.index.cmp(&o.l.index)
     }
 }
@@ -99,7 +104,7 @@ impl PartialOrd for LicenseId {
     }
 }
 
-impl std::ops::Deref for LicenseId {
+impl core::ops::Deref for LicenseId {
     type Target = License;
 
     #[inline]
@@ -253,7 +258,7 @@ impl PartialOrd for ExceptionId {
     }
 }
 
-impl std::ops::Deref for ExceptionId {
+impl core::ops::Deref for ExceptionId {
     type Target = Exception;
 
     #[inline]
@@ -585,7 +590,7 @@ pub fn gnu_license_id(base: &str, or_later: bool) -> Option<LicenseId> {
             v[base.len()..].copy_from_slice(b"-only");
         }
 
-        let Ok(s) = std::str::from_utf8(v.as_slice()) else {
+        let Ok(s) = core::str::from_utf8(v.as_slice()) else {
             // Unreachable, but whatever
             return None;
         };
@@ -645,8 +650,8 @@ pub fn license_version() -> &'static str {
 #[cfg(test)]
 mod test {
     use super::LicenseItem;
-
     use crate::{Expression, license_id};
+    use alloc::string::ToString;
 
     #[test]
     fn gnu_or_later_display() {
diff --git a/src/licensee.rs b/src/licensee.rs
index 6377d55..cd39ecb 100644
--- a/src/licensee.rs
+++ b/src/licensee.rs
@@ -3,7 +3,10 @@ use crate::{
     error::{ParseError, Reason},
     lexer::{Lexer, Token},
 };
-use std::fmt;
+use alloc::borrow::ToOwned;
+use alloc::boxed::Box;
+use alloc::string::String;
+use core::fmt;
 
 /// A convenience wrapper for a license and optional additional text that can be
 /// checked against a license requirement to see if it satisfies the requirement
@@ -26,7 +29,7 @@ impl fmt::Display for Licensee {
     }
 }
 
-impl std::str::FromStr for Licensee {
+impl core::str::FromStr for Licensee {
     type Err = ParseError;
 
     fn from_str(s: &str) -> Result<Self, Self::Err> {
@@ -243,7 +246,7 @@ impl Licensee {
 
 impl PartialOrd<LicenseReq> for Licensee {
     #[inline]
-    fn partial_cmp(&self, o: &LicenseReq) -> Option<std::cmp::Ordering> {
+    fn partial_cmp(&self, o: &LicenseReq) -> Option<core::cmp::Ordering> {
         self.inner.partial_cmp(o)
     }
 }
@@ -267,6 +270,9 @@ mod test {
     use crate::{
         AdditionItem, LicenseItem, LicenseRef, LicenseReq, Licensee, exception_id, license_id,
     };
+    use alloc::borrow::ToOwned;
+    use alloc::boxed::Box;
+    use alloc::vec::Vec;
 
     const LICENSEES: &[&str] = &[
         "LicenseRef-Embark-Proprietary",