diff --git a/.github/workflows/release-build.yml b/.github/workflows/release-build.yml
new file mode 100644
index 0000000..ef11a25
--- /dev/null
+++ b/.github/workflows/release-build.yml
@@ -0,0 +1,76 @@
+name: Release build
+
+on:
+  push:
+    tags:
+      - v[0-9]*
+
+permissions:
+  contents: read
+
+env:
+  UV_FROZEN: "true"
+
+jobs:
+  build:
+    name: Build and attest immutable artifacts
+    runs-on: ubuntu-latest
+    permissions:
+      attestations: write
+      contents: read
+      id-token: write
+    steps:
+      - name: Check out tagged source
+        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@c771a70e6277c0a99b617c7a806ffedaca235ff9 # v9.0.0
+        with:
+          version: 0.12.3
+          enable-cache: true
+
+      - name: Install release environment
+        run: |
+          uv python install 3.11
+          uv sync --group release --group security --python 3.11
+
+      - name: Validate tag and source version
+        env:
+          RELEASE_TAG: ${{ github.ref_name }}
+        run: uv run --python 3.11 python scripts/release.py "$RELEASE_TAG"
+
+      - name: Build once
+        run: uv build --out-dir artifact/release
+
+      - name: Validate distributions
+        env:
+          RELEASE_TAG: ${{ github.ref_name }}
+        run: |
+          uv run --python 3.11 python scripts/release.py "$RELEASE_TAG" --artifacts artifact/release
+          uvx --from twine==7.0.0 twine check artifact/release/*
+          uvx --from check-wheel-contents==0.6.3 check-wheel-contents artifact/release/*.whl
+
+      - name: Generate dependency evidence and CycloneDX SBOM
+        run: |
+          mkdir -p artifact/evidence
+          uv export --no-dev --no-hashes --no-emit-project --output-file artifact/evidence/requirements.txt
+          uvx --from pip-audit==2.10.1 pip-audit --requirement artifact/evidence/requirements.txt --format cyclonedx-json --output artifact/evidence/sbom.cdx.json
+
+      - name: Install and import the built wheel in a clean environment
+        run: |
+          python -m venv "$RUNNER_TEMP/urbanpy-wheel-smoke"
+          "$RUNNER_TEMP/urbanpy-wheel-smoke/bin/python" -m pip install artifact/release/*.whl
+          "$RUNNER_TEMP/urbanpy-wheel-smoke/bin/python" -c "import urbanpy; print(urbanpy.__version__)"
+
+      - name: Attest package provenance
+        uses: actions/attest-build-provenance@4d101475d8b20a2381f78447822ac1eab6504dd8 # v4.2.2
+        with:
+          subject-path: artifact/release/*
+
+      - name: Upload immutable release bundle
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
+        with:
+          name: urbanpy-release-${{ github.ref_name }}
+          path: artifact
+          if-no-files-found: error
+          retention-days: 30
diff --git a/.github/workflows/release-publish.yml b/.github/workflows/release-publish.yml
new file mode 100644
index 0000000..9b67c4e
--- /dev/null
+++ b/.github/workflows/release-publish.yml
@@ -0,0 +1,116 @@
+name: Release publish
+
+on:
+  workflow_dispatch:
+    inputs:
+      build_run_id:
+        description: Successful Release build workflow run ID
+        required: true
+        type: string
+      version:
+        description: Exact package version without the v prefix
+        required: true
+        type: string
+      target:
+        description: Protected trusted-publishing destination
+        required: true
+        type: choice
+        options:
+          - testpypi
+          - pypi
+
+permissions:
+  contents: read
+
+env:
+  UV_FROZEN: "true"
+
+jobs:
+  publish:
+    name: Publish reviewed artifacts to ${{ inputs.target }}
+    runs-on: ubuntu-latest
+    environment: release-${{ inputs.target }}
+    permissions:
+      actions: read
+      contents: read
+      id-token: write
+    steps:
+      - name: Check out the exact release tag
+        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+        with:
+          ref: v${{ inputs.version }}
+
+      - name: Verify source workflow and commit
+        env:
+          GH_TOKEN: ${{ github.token }}
+          RUN_ID: ${{ inputs.build_run_id }}
+        run: |
+          run_json="$(gh api "repos/$GITHUB_REPOSITORY/actions/runs/$RUN_ID")"
+          test "$(jq -r .conclusion <<<"$run_json")" = "success"
+          test "$(jq -r .event <<<"$run_json")" = "push"
+          test "$(jq -r .path <<<"$run_json")" = ".github/workflows/release-build.yml"
+          test "$(jq -r .head_repository.full_name <<<"$run_json")" = "$GITHUB_REPOSITORY"
+          test "$(jq -r .head_sha <<<"$run_json")" = "$(git rev-parse HEAD)"
+
+      - name: Download the immutable build bundle
+        uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
+        with:
+          name: urbanpy-release-v${{ inputs.version }}
+          path: artifact
+          run-id: ${{ inputs.build_run_id }}
+          github-token: ${{ github.token }}
+
+      - name: Install validation environment
+        uses: astral-sh/setup-uv@c771a70e6277c0a99b617c7a806ffedaca235ff9 # v9.0.0
+        with:
+          version: 0.12.3
+
+      - name: Sync locked release tools
+        run: |
+          uv python install 3.11
+          uv sync --group release --python 3.11
+
+      - name: Revalidate tag, target, and artifact contents
+        env:
+          RELEASE_TAG: v${{ inputs.version }}
+          RELEASE_TARGET: ${{ inputs.target }}
+        run: uv run --python 3.11 python scripts/release.py "$RELEASE_TAG" --target "$RELEASE_TARGET" --artifacts artifact/release
+
+      - name: Publish prerelease to TestPyPI with OIDC
+        if: inputs.target == 'testpypi'
+        uses: pypa/gh-action-pypi-publish@dc37677b2e1c63e2034f94d8a5b11f265b73ba33 # v1.14.2
+        with:
+          packages-dir: artifact/release
+          repository-url: https://test.pypi.org/legacy/
+          verbose: true
+
+      - name: Publish stable release to PyPI with OIDC
+        if: inputs.target == 'pypi'
+        uses: pypa/gh-action-pypi-publish@dc37677b2e1c63e2034f94d8a5b11f265b73ba33 # v1.14.2
+        with:
+          packages-dir: artifact/release
+          verbose: true
+
+  github-release:
+    name: Publish GitHub release after PyPI
+    if: inputs.target == 'pypi'
+    needs: publish
+    runs-on: ubuntu-latest
+    environment: release-pypi
+    permissions:
+      actions: read
+      contents: write
+    steps:
+      - name: Download the published build bundle
+        uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
+        with:
+          name: urbanpy-release-v${{ inputs.version }}
+          path: artifact
+          run-id: ${{ inputs.build_run_id }}
+          github-token: ${{ github.token }}
+
+      - name: Create release from the existing protected tag
+        env:
+          GH_TOKEN: ${{ github.token }}
+          RELEASE_TAG: v${{ inputs.version }}
+        run: gh release create "$RELEASE_TAG" artifact/release/* --verify-tag --generate-notes --title "UrbanPy $RELEASE_TAG"
diff --git a/RELEASING.md b/RELEASING.md
new file mode 100644
index 0000000..208c59f
--- /dev/null
+++ b/RELEASING.md
@@ -0,0 +1,60 @@
+# Release runbook
+
+Only a human maintainer may tag, approve, publish, yank, or release UrbanPy.
+Automation builds and verifies artifacts but never chooses to release them.
+
+## One-time trusted-publishing setup
+
+Repository and PyPI administrators must create protected GitHub environments
+named `release-testpypi` and `release-pypi`, require designated maintainer
+reviewers, prevent self-review, and restrict deployment to protected `v*` tags.
+Configure matching trusted publishers on TestPyPI and PyPI for
+`release-publish.yml` and the exact environment name. Do not add API tokens.
+
+Protect release tags and require the same human review, CI, mandatory SonarQube,
+security, and dependency-compliance gates used for the default branch. These are
+administrator actions and are intentionally not performed by coding agents.
+
+## Prerelease procedure
+
+1. Reconcile `CHANGELOG.md`, version metadata, deprecations, and migration docs.
+2. Confirm supported Python CI, docs, package, vulnerability, license, and
+   mandatory SonarQube checks are green on the reviewed commit.
+3. Set an alpha, beta, or release-candidate version and merge through normal
+   review. A maintainer creates the matching protected tag, such as `v0.3.0rc1`.
+4. `release-build.yml` validates the tag, builds once, inspects the artifacts,
+   creates a CycloneDX SBOM, runs a clean install, attests provenance, and stores
+   one immutable bundle.
+5. Inspect the build log, SBOM, provenance, wheel/sdist, and artifact run ID.
+6. Dispatch `release-publish.yml` with that run ID, exact version, and
+   `testpypi`. A protected-environment reviewer approves OIDC publication.
+7. Install from TestPyPI in a clean environment and exercise imports, a local
+   geometry workflow, canonical Geofabrik resolution, and the documented OSRM
+   smoke test on each claimed platform.
+
+The workflow rejects prerelease versions sent to production PyPI.
+
+## Stable release procedure
+
+Repeat the review with a stable version and protected tag. Dispatch publish with
+target `pypi`. The exact already-built artifacts are promoted through OIDC; no
+build occurs in the publish job. After PyPI succeeds, the workflow creates the
+GitHub release from the same bundle and existing tag.
+
+Deploy versioned documentation from the released version only after package
+publication and smoke tests succeed. Submit a conda-forge recipe after the stable
+PyPI artifact has community validation; do not maintain a private Conda publish
+workflow.
+
+## Failure, rollback, and post-release
+
+- Before publication, abandon the tag and create a corrected version; never
+  replace artifacts under an existing version.
+- After publication, yank only for security, data-loss, installation, or severe
+  correctness defects. Publish a fixed patch; do not silently overwrite files.
+- Use a private security advisory and coordinated disclosure for vulnerabilities.
+- Record the incident, affected versions, mitigations, and upgrade path in the
+  changelog and GitHub release.
+- For four weeks, monitor installation failures, provider contracts, security
+  reports, dependency alerts, and OSRM platform evidence. Assign an accountable
+  maintainer before starting the release.
diff --git a/pyproject.toml b/pyproject.toml
index b3d81ef..4b60854 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -86,6 +86,7 @@ docs = [
 release = [
   "build>=1.2",
   "check-wheel-contents>=0.6",
+  "packaging>=24",
   "twine>=6",
 ]
 security = [
@@ -108,6 +109,7 @@ include = [
   "/GOVERNANCE.md",
   "/LICENSE",
   "/README.md",
+  "/RELEASING.md",
   "/SECURITY.md",
   "/SUPPORT.md",
   "/docs",
diff --git a/scripts/release.py b/scripts/release.py
new file mode 100644
index 0000000..e2554f2
--- /dev/null
+++ b/scripts/release.py
@@ -0,0 +1,103 @@
+"""Validate immutable UrbanPy release inputs without mutating source files."""
+
+from __future__ import annotations
+
+import argparse
+import email.parser
+import sys
+import tarfile
+import tomllib
+import zipfile
+from pathlib import Path
+
+from packaging.version import Version
+
+
+class ReleaseValidationError(ValueError):
+    """A release input is inconsistent or unsafe to publish."""
+
+
+def project_version(pyproject: Path = Path("pyproject.toml")) -> Version:
+    with pyproject.open("rb") as source:
+        value = tomllib.load(source)["project"]["version"]
+    return Version(value)
+
+
+def validate_tag(tag: str, *, pyproject: Path = Path("pyproject.toml")) -> Version:
+    if not tag.startswith("v"):
+        raise ReleaseValidationError("release tags must start with 'v'")
+    tagged = Version(tag[1:])
+    declared = project_version(pyproject)
+    if tagged != declared:
+        raise ReleaseValidationError(
+            f"tag version {tagged} does not match project version {declared}"
+        )
+    return declared
+
+
+def validate_artifacts(directory: Path, expected: Version) -> None:
+    wheels = sorted(directory.glob("urbanpy-*.whl"))
+    sdists = sorted(directory.glob("urbanpy-*.tar.gz"))
+    if len(wheels) != 1 or len(sdists) != 1:
+        raise ReleaseValidationError("expected exactly one UrbanPy wheel and one sdist")
+    wheel_version = _wheel_version(wheels[0])
+    sdist_version = _sdist_version(sdists[0])
+    if wheel_version != expected or sdist_version != expected:
+        raise ReleaseValidationError(
+            "wheel, sdist, and requested release versions must match"
+        )
+
+
+def validate_target(version: Version, target: str) -> None:
+    if target not in {"pypi", "testpypi"}:
+        raise ReleaseValidationError("target must be pypi or testpypi")
+    if target == "pypi" and (version.is_prerelease or version.is_devrelease):
+        raise ReleaseValidationError("prereleases must be exercised on TestPyPI")
+
+
+def _wheel_version(path: Path) -> Version:
+    with zipfile.ZipFile(path) as archive:
+        metadata_names = [
+            name for name in archive.namelist() if name.endswith(".dist-info/METADATA")
+        ]
+        if len(metadata_names) != 1:
+            raise ReleaseValidationError("wheel must contain exactly one METADATA file")
+        message = email.parser.BytesParser().parsebytes(archive.read(metadata_names[0]))
+    if message.get("Name") != "urbanpy":
+        raise ReleaseValidationError("wheel project name is not urbanpy")
+    return Version(message["Version"])
+
+
+def _sdist_version(path: Path) -> Version:
+    with tarfile.open(path, "r:gz") as archive:
+        roots = {name.split("/", 1)[0] for name in archive.getnames() if name}
+    if len(roots) != 1:
+        raise ReleaseValidationError("sdist must contain exactly one root directory")
+    root = roots.pop()
+    prefix = "urbanpy-"
+    if not root.startswith(prefix):
+        raise ReleaseValidationError("sdist root must use the UrbanPy project name")
+    return Version(root.removeprefix(prefix))
+
+
+def main(argv: list[str] | None = None) -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument("tag")
+    parser.add_argument("--artifacts", type=Path)
+    parser.add_argument("--target", choices=("pypi", "testpypi"))
+    args = parser.parse_args(argv)
+    try:
+        version = validate_tag(args.tag)
+        if args.artifacts:
+            validate_artifacts(args.artifacts, version)
+        if args.target:
+            validate_target(version, args.target)
+    except (ReleaseValidationError, OSError, KeyError) as error:
+        print(f"release validation failed: {error}", file=sys.stderr)
+        return 2
+    print(f"validated UrbanPy {version}")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/tests/release_test.py b/tests/release_test.py
new file mode 100644
index 0000000..dfdea0d
--- /dev/null
+++ b/tests/release_test.py
@@ -0,0 +1,53 @@
+import tarfile
+import zipfile
+from pathlib import Path
+
+import pytest
+from packaging.version import Version
+
+from scripts.release import (
+    ReleaseValidationError,
+    validate_artifacts,
+    validate_tag,
+    validate_target,
+)
+
+
+def _pyproject(path: Path, version: str) -> Path:
+    path.write_text(f'[project]\nname = "urbanpy"\nversion = "{version}"\n')
+    return path
+
+
+def test_tag_must_exactly_match_declared_version(tmp_path):
+    pyproject = _pyproject(tmp_path / "pyproject.toml", "0.3.0a1")
+
+    assert validate_tag("v0.3.0a1", pyproject=pyproject) == Version("0.3.0a1")
+    with pytest.raises(ReleaseValidationError, match="does not match"):
+        validate_tag("v0.3.0a2", pyproject=pyproject)
+    with pytest.raises(ReleaseValidationError, match="start with"):
+        validate_tag("0.3.0a1", pyproject=pyproject)
+
+
+def test_prereleases_cannot_publish_to_production_pypi():
+    validate_target(Version("0.3.0a1"), "testpypi")
+    validate_target(Version("0.3.0"), "pypi")
+    with pytest.raises(ReleaseValidationError, match="TestPyPI"):
+        validate_target(Version("0.3.0rc1"), "pypi")
+
+
+def test_artifact_versions_are_read_from_contents_not_filenames(tmp_path):
+    wheel = tmp_path / "urbanpy-0.3.0-py3-none-any.whl"
+    with zipfile.ZipFile(wheel, "w") as archive:
+        archive.writestr(
+            "urbanpy-0.3.0.dist-info/METADATA",
+            "Metadata-Version: 2.4\nName: urbanpy\nVersion: 0.3.0\n",
+        )
+    sdist = tmp_path / "urbanpy-0.3.0.tar.gz"
+    with tarfile.open(sdist, "w:gz") as archive:
+        placeholder = tmp_path / "pyproject.toml"
+        placeholder.write_text("[project]\n")
+        archive.add(placeholder, arcname="urbanpy-0.3.0/pyproject.toml")
+
+    validate_artifacts(tmp_path, Version("0.3.0"))
+    with pytest.raises(ReleaseValidationError, match="must match"):
+        validate_artifacts(tmp_path, Version("0.3.1"))
diff --git a/uv.lock b/uv.lock
index ec622eb..62b4a03 100644
--- a/uv.lock
+++ b/uv.lock
@@ -3476,6 +3476,7 @@ lint = [
 release = [
     { name = "build" },
     { name = "check-wheel-contents" },
+    { name = "packaging" },
     { name = "twine" },
 ]
 security = [
@@ -3538,6 +3539,7 @@ lint = [
 release = [
     { name = "build", specifier = ">=1.2" },
     { name = "check-wheel-contents", specifier = ">=0.6" },
+    { name = "packaging", specifier = ">=24" },
     { name = "twine", specifier = ">=6" },
 ]
 security = [{ name = "pip-audit", specifier = ">=2.7" }]