diff --git a/.gitignore b/.gitignore
index 47ad4b1..fcbb5dd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,5 @@
 # Add any project-specific files here:
-
+sniffio/_version.py
 
 # Sphinx docs
 docs/build/
diff --git a/ci.sh b/ci.sh
index bab85fc..afa8a5a 100755
--- a/ci.sh
+++ b/ci.sh
@@ -10,7 +10,7 @@ pip install -U pip setuptools wheel
 
 if [ "$CHECK_FORMATTING" = "1" ]; then
     pip install yapf==${YAPF_VERSION}
-    if ! yapf -rpd setup.py sniffio; then
+    if ! yapf -rpd sniffio; then
         cat <<EOF
 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
@@ -18,7 +18,7 @@ if [ "$CHECK_FORMATTING" = "1" ]; then
 Formatting problems were found (listed above). To fix them, run
 
    pip install yapf==${YAPF_VERSION}
-   yapf -rpi setup.py sniffio
+   yapf -rpi sniffio
 
 in your local checkout.
 
@@ -43,8 +43,8 @@ EOF
     exit 0
 fi
 
-python setup.py sdist --formats=zip
-pip install dist/*.zip
+python -m build -nsx .
+pip install dist/*.tar.gz
 
 # Actual tests
 pip install -Ur test-requirements.txt
diff --git a/newsfragments/33.feature.rst b/newsfragments/33.feature.rst
new file mode 100644
index 0000000..508e13b
--- /dev/null
+++ b/newsfragments/33.feature.rst
@@ -0,0 +1 @@
+Moved the metadata into ``PEP 621``-compliant ``pyproject.toml``.
diff --git a/pyproject.toml b/pyproject.toml
index 6414b3e..64cf62a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,3 +1,48 @@
+[build-system]
+requires = ["setuptools>=61.2", "setuptools_scm[toml]>=3.4.3"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "sniffio"
+authors = [{name = "Nathaniel J. Smith", email = "njs@pobox.com"}]
+license = {text = "MIT OR Apache-2.0"}
+description = "Sniff out which async library your code is running under"
+readme = "README.rst"
+keywords = ["async", "trio", "asyncio"]
+classifiers = [
+    "License :: OSI Approved :: MIT License",
+    "License :: OSI Approved :: Apache Software License",
+    "Framework :: Trio",
+    "Framework :: AsyncIO",
+    "Operating System :: POSIX :: Linux",
+    "Operating System :: MacOS :: MacOS X",
+    "Operating System :: Microsoft :: Windows",
+    "Programming Language :: Python :: 3 :: Only",
+    "Programming Language :: Python :: Implementation :: CPython",
+    "Programming Language :: Python :: Implementation :: PyPy",
+    "Intended Audience :: Developers",
+    "Development Status :: 5 - Production/Stable",
+]
+urls = {Homepage = "https://github.com/python-trio/sniffio"}
+requires-python = ">=3.7"
+dynamic = ["version"]
+
+[project.optional-dependencies]
+testing = ["curio"]
+
+[tool.setuptools]
+include-package-data = false
+
+[tool.setuptools.packages]
+find = {namespaces = false}
+
+[tool.setuptools.package-data]
+sniffio = ["py.typed"]
+
+[tool.setuptools_scm]
+write_to = "sniffio/_version.py"
+write_to_template = "__version__ = \"{version}\"\n"
+
 [tool.towncrier]
 package = "sniffio"
 filename = "docs/source/history.rst"
diff --git a/setup.py b/setup.py
deleted file mode 100644
index 374839c..0000000
--- a/setup.py
+++ /dev/null
@@ -1,39 +0,0 @@
-from setuptools import setup, find_packages
-
-exec(open("sniffio/_version.py", encoding="utf-8").read())
-
-LONG_DESC = open("README.rst", encoding="utf-8").read()
-
-setup(
-    name="sniffio",
-    version=__version__,
-    description="Sniff out which async library your code is running under",
-    url="https://github.com/python-trio/sniffio",
-    long_description=LONG_DESC,
-    author="Nathaniel J. Smith",
-    author_email="njs@pobox.com",
-    license="MIT OR Apache-2.0",
-    packages=find_packages(),
-    package_data={"sniffio": ["py.typed"]},
-    keywords=[
-        "async",
-        "trio",
-        "asyncio",
-    ],
-    python_requires=">=3.7",
-    tests_require=['curio'],
-    classifiers=[
-        "License :: OSI Approved :: MIT License",
-        "License :: OSI Approved :: Apache Software License",
-        "Framework :: Trio",
-        "Framework :: AsyncIO",
-        "Operating System :: POSIX :: Linux",
-        "Operating System :: MacOS :: MacOS X",
-        "Operating System :: Microsoft :: Windows",
-        "Programming Language :: Python :: 3 :: Only",
-        "Programming Language :: Python :: Implementation :: CPython",
-        "Programming Language :: Python :: Implementation :: PyPy",
-        "Intended Audience :: Developers",
-        "Development Status :: 5 - Production/Stable",
-    ],
-)
diff --git a/sniffio/_version.py b/sniffio/_version.py
deleted file mode 100644
index 0de77e3..0000000
--- a/sniffio/_version.py
+++ /dev/null
@@ -1,3 +0,0 @@
-# This file is imported from __init__.py and exec'd from setup.py
-
-__version__ = "1.3.0+dev"