diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 77109b428..e0968df6a 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -73,10 +73,15 @@ jobs:
           cache: pip
           cache-dependency-path: |
             requirements.txt
-            dev-requirements.txt
+            pyproject.toml
+
+      - name: Upgrade pip
+        run: python -m pip install --upgrade pip
 
       - name: Install dependencies
-        run: pip install -r requirements.txt -r dev-requirements.txt
+        run: |
+          pip install -r requirements.txt
+          pip install --group dev
 
       - name: Check format
         continue-on-error: ${{inputs.soft-linting == 'true'}}
@@ -237,10 +242,15 @@ jobs:
           cache: pip
           cache-dependency-path: |
             requirements.txt
-            dev-requirements.txt
+            pyproject.toml
+
+      - name: Upgrade pip
+        run: python -m pip install --upgrade pip
 
       - name: Install dependencies
-        run: pip install -r requirements.txt -r dev-requirements.txt
+        run: |
+          pip install -r requirements.txt
+          pip install --group dev
 
       - name: Set up Bazel
         uses: './.github/actions/set-up-bazel'
@@ -322,10 +332,15 @@ jobs:
           cache: pip
           cache-dependency-path: |
             requirements.txt
-            dev-requirements.txt
+            pyproject.toml
+
+      - name: Upgrade pip
+        run: python -m pip install --upgrade pip
 
       - name: Install dependencies
-        run: pip install -r requirements.txt -r dev-requirements.txt
+        run: |
+          pip install -r requirements.txt
+          pip install --group dev
 
       - name: Set up Bazel
         uses: './.github/actions/set-up-bazel'
@@ -377,10 +392,15 @@ jobs:
           cache: pip
           cache-dependency-path: |
             requirements.txt
-            dev-requirements.txt
+            pyproject.toml
+
+      - name: Upgrade pip
+        run: python -m pip install --upgrade pip
 
       - name: Install dependencies
-        run: pip install -r requirements.txt -r dev-requirements.txt
+        run: |
+          pip install -r requirements.txt
+          pip install --group dev
 
       - name: Set up Bazel
         uses: './.github/actions/set-up-bazel'
diff --git a/.github/workflows/cirq_compatibility.yml b/.github/workflows/cirq_compatibility.yml
index 5fc76ff0f..18d974bef 100644
--- a/.github/workflows/cirq_compatibility.yml
+++ b/.github/workflows/cirq_compatibility.yml
@@ -52,7 +52,7 @@ jobs:
           cache: pip
           cache-dependency-path: |
             requirements.txt
-            dev-requirements.txt
+            pyproject.toml
 
       - name: Install latest dev version of Cirq
         run: pip install --upgrade cirq~=1.0.dev
@@ -60,7 +60,7 @@ jobs:
       - name: Install qsim dev requirements
         run: |
           pip install -r requirements.txt
-          pip install -r dev-requirements.txt
+          pip install --group dev
 
       - name: Run Python tests
         env:
diff --git a/Dockerfile b/Dockerfile
index 7d82f2eb5..100c68e92 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -38,21 +38,23 @@ COPY ./lib/ /qsim/lib/
 COPY ./pybind_interface/ /qsim/lib/
 COPY ./qsimcirq_tests/ /qsim/qsimcirq_tests/
 COPY ./requirements.txt /qsim/requirements.txt
-COPY ./dev-requirements.txt /qsim/dev-requirements.txt
+COPY ./pyproject.toml /qsim/pyproject.toml
 
 # Create venv to avoid collision between system packages and what we install.
-RUN python3 -m venv --upgrade-deps test_env
+RUN python3 -m venv --upgrade-deps test_env && \
+    . test_env/bin/activate
+
+WORKDIR /qsim/
 
 # Activate venv.
 ENV PATH="/test_env/bin:$PATH"
 
 # Install qsim requirements.
-# hadolint ignore=DL3042
-RUN python3 -m pip install -r /qsim/requirements.txt && \
-    python3 -m pip install -r /qsim/dev-requirements.txt
+# hadolint ignore=DL3013
+RUN python3 -m pip install --no-cache-dir --upgrade pip && \
+    python3 -m pip install --no-cache-dir -r requirements.txt
 
 # Compile qsim.
-WORKDIR /qsim/
 RUN make -j qsim
 
 ENTRYPOINT ["/qsim/apps/qsim_base.x"]
diff --git a/MANIFEST.in b/MANIFEST.in
index 4b487267f..2968589be 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -1,5 +1,4 @@
 include requirements.txt
-include dev-requirements.txt
 include CMakeLists.txt
 
 graft pybind_interface
diff --git a/dev-requirements.txt b/dev-requirements.txt
deleted file mode 100644
index 2a0fc0a36..000000000
--- a/dev-requirements.txt
+++ /dev/null
@@ -1,12 +0,0 @@
-cmake~=3.28.1
-black~=25.9.0
-flynt~=1.0
-isort[colors]~=6.0.1
-# The global option to pybind11 makes it include CMake files in a location where
-# CMake will find them. It makes a crucial difference in some environments.
-pybind11[global]
-pylint~=4.0.2
-pytest
-pytest-xdist
-py-cpuinfo
-setuptools>=78.1.1
diff --git a/docs/install_qsimcirq.md b/docs/install_qsimcirq.md
index 6887a57f1..441dc3ead 100644
--- a/docs/install_qsimcirq.md
+++ b/docs/install_qsimcirq.md
@@ -10,18 +10,24 @@ directly in C++ code without building and installing the qsimcirq interface.
 
 ## Before installation
 
-Prior to installation, consider opening a
+Prior to installation, consider creating a
 [virtual environment](https://packaging.python.org/guides/installing-using-pip-and-virtual-environments/).
 
-Prerequisites are included in the
+Prerequisites for installing and running qsim are included in the
 [`requirements.txt`](https://github.com/quantumlib/qsim/blob/main/requirements.txt)
-file, and will be automatically installed along with qsimcirq.
+file, and will be automatically installed along with qsimcirq when you install
+it with pip.
 
-If you'd like to develop qsimcirq, a separate set of dependencies are includes
+If you'd like to develop qsimcirq, a separate set of dependencies are defined
 in the
-[`dev-requirements.txt`](https://github.com/quantumlib/qsim/blob/main/dev-requirements.txt)
-file. You can install them with `pip3 install -r dev-requirements.txt` or
-`pip3 install qsimcirq[dev]`.
+[`pyproject.toml`](https://github.com/quantumlib/qsim/blob/main/pyproject.toml)
+file. Using pip version 25.1 or higher, you can install them with the following
+commands:
+
+```shell
+pip install -r requirements.txt
+pip install --group dev
+```
 
 ## Linux installation
 
diff --git a/pybind_interface/Dockerfile b/pybind_interface/Dockerfile
index 54a4ff511..2b1cb4fd0 100644
--- a/pybind_interface/Dockerfile
+++ b/pybind_interface/Dockerfile
@@ -26,5 +26,9 @@ WORKDIR /qsim/
 # Build pybind code early to cache the results
 RUN make -j -C /qsim/ pybind
 
+# Install Python development dependencies.
+# hadolint ignore=DL3013
+RUN pip install --no-cache-dir --group dev
+
 # Compile and run qsim tests
 ENTRYPOINT ["make", "-C", "/qsim/", "run-py-tests"]
diff --git a/pyproject.toml b/pyproject.toml
index 37d714455..a4f3e4613 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -12,28 +12,135 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+# Note: there are altogether 3 types of dependencies listed in this file:
+#
+#  [build-system].requires: the packages needed for the build system. This list
+#  is not stored in the package metadata.
+#
+#  [project].dependencies: other packages are minimally needed to be able to
+#  install and run qsimcirq. These are things like Cirq, NumPy, etc. Equivalent
+#  to "install_requires" in setuptools' setup.py. The list gets stored in the
+#  metadata of the package; when the project is installed by pip, this is the
+#  specification that is used to install its dependencies.
+#
+#  [dependency-groups].dev: the development dependencies; i.e., what a
+#  developer needs in order to run unit tests, linters, and formatters. The
+#  "[dependency-groups]" section is a Python packaging feature introduced in
+#  2025. This list is not stored in the metadata of the package. To install the
+#  development dependencies, use "pip install --group dev".
+
 [build-system]
+build-backend = "setuptools.build_meta"
 requires = [
-  "packaging",
-  "setuptools>=78.1.1",
-  "pybind11[global]",
-  # "pip install" from sources needs to build Pybind, which needs CMake too.
-  "cmake~=3.28.1",
+    "setuptools>=78.1.1",
+    "setuptools-scm[toml]>=6.2",
+    "wheel",
 ]
-build-backend = "setuptools.build_meta"
+
+[project]
+name = "qsimcirq"
+description = "High-performance quantum circuit simulator for C++ and Python."
+authors = [
+    { name = "The qsim/qsimh Developers", email = "qsim-qsimh-dev@googlegroups.com" }
+]
+maintainers = [
+    { name = "Google Quantum AI", email = "quantum-oss-maintainers@google.com" }
+]
+readme = {file = "README.md", content-type = "text/markdown"}
+license = "Apache-2.0"
+requires-python = ">=3.10.0"
+dynamic = ["version", "dependencies"]
+classifiers = [
+    "Development Status :: 5 - Production/Stable",
+    "Environment :: GPU :: NVIDIA CUDA",
+    "Intended Audience :: Developers",
+    "Intended Audience :: Science/Research",
+    "Operating System :: MacOS :: MacOS X",
+    "Operating System :: Microsoft :: Windows",
+    "Operating System :: POSIX :: Linux",
+    "Programming Language :: C++",
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.10",
+    "Programming Language :: Python :: 3.11",
+    "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
+    "Topic :: Scientific/Engineering :: Quantum Computing",
+    "Topic :: Software Development :: Libraries :: Python Modules",
+    "Typing :: Typed",
+]
+keywords = [
+    "algorithms",
+    "cirq",
+    "nisq",
+    "quantum algorithm development",
+    "quantum circuit simulator",
+    "quantum computer simulator",
+    "quantum computing",
+    "quantum programming",
+    "quantum simulation",
+    "quantum",
+    "schrödinger-feynman simulation",
+    "simulation",
+    "state vector simulator",
+]
+
+[project.urls]
+documentation = "https://quantumai.google/qsim"
+download = "https://pypi.org/project/qsimcirq/#files"
+homepage = "https://quantumai.google/qsim"
+issues = "https://github.com/quantumlib/qsim/issues"
+source = "https://github.com/quantumlib/qsim"
+
+[dependency-groups]
+# Development dependencies. Install these with "pip install --group dev".
+dev = [
+    "black~=25.9.0",
+    "cibuildwheel",
+    # Distutils was removed from Python in 3.12.
+    "setuptools; python_version >= '3.12'",
+    "flynt~=1.0",
+    "isort[colors]~=6.0.1",
+    "py-cpuinfo",
+    "pylint~=4.0.2",
+    "pytest",
+    "pytest-xdist",
+]
+
+[tool.setuptools]
+packages = ["qsimcirq"]
+package-data = {"qsimcirq" = ["py.typed"]}
+
+[tool.setuptools.dynamic]
+# The next one becomes the value of [project].version.
+version = {attr = "qsimcirq._version.__version__"}
+# The next one becomes [project].dependencies, equivalent to "install_requires"
+# in setuptools' setup.py. "pip install qsim" installs these automatically.
+dependencies = {file = ["requirements.txt"] }
 
 [tool.cibuildwheel]
-test-extras = "dev"
+build = "cp310-* cp311-* cp312-* cp313-*"
 dependency-versions = "latest"
 enable = ["cpython-prerelease"]
 environment.PIP_PREFER_BINARY = "1"
 # Due to package & module name conflict, temporarily move it away to run tests:
-before-test = "mv {package}/qsimcirq /tmp"
-test-command = "pytest -s -v {package}/qsimcirq_tests/qsimcirq_test.py && mv /tmp/qsimcirq {package}"
+before-test = "pip install --group dev && mv {package}/qsimcirq /tmp"
+test-command = """
+pytest -s -v {package}/qsimcirq_tests/qsimcirq_test.py &&
+mv /tmp/qsimcirq {package}
+"""
 
 [tool.cibuildwheel.macos]
-before-build = "brew install -q libomp llvm@19 && brew unlink libomp && brew unlink llvm@19 && brew link --force libomp && brew link --force llvm@19"
-repair-wheel-command = "delocate-listdeps {wheel} && delocate-wheel --verbose --require-archs {delocate_archs} -w {dest_dir} {wheel}"
+before-build = """
+brew install -q libomp llvm@19 &&
+brew unlink libomp &&
+brew unlink llvm@19 &&
+brew link --force libomp &&
+brew link --force llvm@19
+"""
+repair-wheel-command = """
+delocate-listdeps {wheel} &&
+delocate-wheel --verbose --require-archs {delocate_archs} -w {dest_dir} {wheel}
+"""
 
 [tool.cibuildwheel.linux]
 manylinux-x86_64-image = "manylinux2014"
diff --git a/requirements.txt b/requirements.txt
index 21e8a4ade..a927b3363 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,17 @@
+# Installation and run-time dependencies for qsimcirq. This file is read
+# by pyproject.toml.
+
 absl-py
 cirq-core~=1.0
-numpy>=1.26.0
+numpy>=1.26.0,<2.0; python_version < '3.11'
+numpy>=2.0; python_version >= '3.11'
+
+# These are needed because installing qsimcirq in some environments may require
+# pip to compile Pybind for that specific platform:
+cmake~=3.28.1
+pybind11[global]
+
+# These are transitive dependencies we need to constrain to avoid unresolvable
+# installation conflicts due to them requiring higher Python versions:
+scipy<1.16; python_version < '3.11'
+contourpy<1.3; python_version < '3.11'
diff --git a/setup.py b/setup.py
index 328b27cdd..d3ccfa54c 100644
--- a/setup.py
+++ b/setup.py
@@ -24,6 +24,10 @@
 from setuptools import Extension, setup
 from setuptools.command.build_ext import build_ext
 
+# qsimcirq/_version.py contains the source of truth for the version nhumber.
+__version__ = runpy.run_path("qsimcirq/_version.py")["__version__"]
+assert __version__, "The version string must not be empty"
+
 
 class CMakeExtension(Extension):
     def __init__(self, name, sourcedir=""):
@@ -67,6 +71,8 @@ def build_extension(self, ext):
                 "-DCMAKE_CUDA_COMPILER=nvcc",
             ]
 
+        # Append additional CMake arguments from the environment variable.
+        # This is e.g. used by cibuildwheel to force a certain C++ standard.
         additional_cmake_args = os.environ.get("CMAKE_ARGS", "")
         if additional_cmake_args:
             cmake_args += additional_cmake_args.split()
@@ -110,9 +116,7 @@ def build_extension(self, ext):
 
         env = os.environ.copy()
         cxxflags = env.get("CXXFLAGS", "")
-        env["CXXFLAGS"] = (
-            f'{cxxflags} -DVERSION_INFO=\\"{self.distribution.get_version()}\\"'
-        )
+        env["CXXFLAGS"] = f'{cxxflags} -DVERSION_INFO=\\"{__version__}\\"'
         if not os.path.exists(self.build_temp):
             os.makedirs(self.build_temp)
         subprocess.check_call(
@@ -124,42 +128,7 @@ def build_extension(self, ext):
         )
 
 
-with open("requirements.txt") as f:
-    requirements = [
-        line.strip() for line in f if line.strip() and not line.strip().startswith("#")
-    ]
-with open("dev-requirements.txt") as f:
-    dev_requirements = [
-        line.strip() for line in f if line.strip() and not line.strip().startswith("#")
-    ]
-
-description = "Schrödinger and Schrödinger-Feynman simulators for quantum circuits."
-
-# README file as long_description.
-with open("README.md", encoding="utf-8") as f:
-    long_description = f.read()
-
-__version__ = runpy.run_path("qsimcirq/_version.py")["__version__"]
-if not __version__:
-    raise ValueError("Version string cannot be empty")
-
 setup(
-    name="qsimcirq",
-    version=__version__,
-    url="https://github.com/quantumlib/qsim",
-    author="The qsim/qsimh Developers",
-    author_email="qsim-qsimh-dev@googlegroups.com",
-    maintainer="Google Quantum AI",
-    maintainer_email="quantum-oss-maintainers@google.com",
-    python_requires=">=3.10.0",
-    install_requires=requirements,
-    extras_require={
-        "dev": dev_requirements,
-    },
-    license="Apache-2.0",
-    description=description,
-    long_description=long_description,
-    long_description_content_type="text/markdown",
     ext_modules=[
         CMakeExtension("qsimcirq/qsim_avx512"),
         CMakeExtension("qsimcirq/qsim_avx2"),
@@ -170,49 +139,5 @@ def build_extension(self, ext):
         CMakeExtension("qsimcirq/qsim_decide"),
         CMakeExtension("qsimcirq/qsim_hip"),
     ],
-    cmdclass=dict(build_ext=CMakeBuild),
-    zip_safe=False,
-    packages=["qsimcirq"],
-    package_data={"qsimcirq": ["py.typed"]},
-    classifiers=[
-        "Development Status :: 5 - Production/Stable",
-        "Environment :: GPU :: NVIDIA CUDA",
-        "Intended Audience :: Developers",
-        "Intended Audience :: Science/Research",
-        "Operating System :: MacOS :: MacOS X",
-        "Operating System :: Microsoft :: Windows",
-        "Operating System :: POSIX :: Linux",
-        "Programming Language :: C++",
-        "Programming Language :: Python :: 3",
-        "Programming Language :: Python :: 3.10",
-        "Programming Language :: Python :: 3.11",
-        "Programming Language :: Python :: 3.12",
-        "Programming Language :: Python :: 3.13",
-        "Topic :: Scientific/Engineering :: Quantum Computing",
-        "Topic :: Software Development :: Libraries :: Python Modules",
-        "Typing :: Typed",
-    ],
-    keywords=[
-        "algorithms",
-        "api",
-        "application programming interface",
-        "cirq",
-        "google quantum",
-        "google",
-        "nisq",
-        "python",
-        "quantum algorithm development",
-        "quantum circuit simulator",
-        "quantum computer simulator",
-        "quantum computing",
-        "quantum computing research",
-        "quantum programming",
-        "quantum simulation",
-        "quantum",
-        "schrödinger-feynman simulation",
-        "sdk",
-        "simulation",
-        "state vector simulator",
-        "software development kit",
-    ],
+    cmdclass={"build_ext": CMakeBuild},
 )