diff --git a/release.py b/release.py
new file mode 100755
index 0000000..749207a
--- /dev/null
+++ b/release.py
@@ -0,0 +1,110 @@
+#!/usr/bin/env python3
+
+"""Write the VERSION file and push to the release branch."""
+
+from __future__ import annotations
+
+import dataclasses
+import datetime
+import logging
+import shlex
+import subprocess
+import sys
+from pathlib import Path
+
+HERE = Path(__file__).resolve().parent
+VERSION_FILE = HERE / "VERSION"
+
+
+def run(argv, **kwargs) -> subprocess.CompletedProcess:
+    kwargs.setdefault("cwd", HERE)
+    kwargs.setdefault("check", True)
+    kwargs.setdefault("encoding", "utf-8")
+    logging.info("Run command: %s", " ".join(shlex.quote(x) for x in argv))
+    return subprocess.run(argv, **kwargs)
+
+
+@dataclasses.dataclass(frozen=True)
+class Version:
+    year: int
+    month: int
+    day: int
+    rel: int = 0
+    suffix: str = ""
+
+    @classmethod
+    def read(cls) -> Version:
+        components = VERSION_FILE.read_text(encoding="ascii").split(".")
+        year = int(components[0])
+        month = int(components[1])
+        day = int(components[2])
+        rel = 0
+        suffix = ""
+        try:
+            rel = int(components[3])
+        except ValueError:
+            suffix = components[3].strip()
+        else:
+            if len(components) > 4:
+                suffix = components[4].strip()
+        return cls(year=year, month=month, day=day, rel=rel, suffix=suffix)
+
+    def write(self, commit: bool = True) -> None:
+        VERSION_FILE.write_text(f"{self}\n", encoding="ascii")
+        logging.info("Wrote version: %s", self)
+        if commit:
+            run(["git", "add", VERSION_FILE.name])
+            run(["git", "commit", "-m", f"Update VERSION to {self}"])
+
+    @classmethod
+    def today(cls) -> Version:
+        today = datetime.date.today()
+        return cls(year=today.year, month=today.month, day=today.day)
+
+    @property
+    def is_today(self):
+        today = datetime.date.today()
+        return (
+            self.year == today.year
+            and self.month == today.month
+            and self.day == today.day
+        )
+
+    def __str__(self):
+        result = f"{self.year}.{self.month:>02}.{self.day:>02}.{self.rel}"
+        if self.suffix:
+            result += f".{self.suffix}"
+        return result
+
+
+def main():
+    upstream = run(
+        ["git", "rev-parse", "--abbrev-ref", "--symbolic-full-name", "@{u}"],
+        stdout=subprocess.PIPE,
+    ).stdout.strip()
+    if upstream != "origin/main":
+        logging.error("Upstream must be origin/main")
+        sys.exit(1)
+    if run(
+        ["git", "diff", "--name-only", "--cached"],
+        stdout=subprocess.PIPE,
+    ).stdout:
+        logging.error("Uncommitted changes exist")
+        sys.exit(1)
+    current_version = Version.read()
+    if current_version.is_today:
+        release_version = dataclasses.replace(
+            current_version, rel=current_version.rel + 1, suffix=""
+        )
+    else:
+        release_version = Version.today()
+    dev_version = dataclasses.replace(release_version, suffix="dev0")
+    release_version.write()
+    run(["git", "tag", str(release_version)])
+    run(["git", "push", "--tags", "origin", "HEAD:refs/heads/release"])
+    dev_version.write()
+    run(["git", "push"])
+
+
+if __name__ == "__main__":
+    main()