diff --git a/.github/workflows/update-changelog.yml b/.github/workflows/update-changelog.yml
new file mode 100644
index 00000000..b13e32cf
--- /dev/null
+++ b/.github/workflows/update-changelog.yml
@@ -0,0 +1,52 @@
+name: Update Changelog
+
+on:
+  pull_request:
+    types: [opened, edited]
+
+jobs:
+  update-changelog:
+    # Only run if this is not a PR from a fork to avoid permission issues
+    # and not a commit made by GitHub Action to avoid infinite loops
+    if: github.event.pull_request.head.repo.full_name == github.repository && github.actor != 'github-actions[bot]'
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
+    
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          # Checkout the PR head ref
+          ref: ${{ github.event.pull_request.head.ref }}
+          token: ${{ secrets.GITHUB_TOKEN }}
+      
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+      
+      - name: Update changelog
+        run: |
+          python modify_changelog.py update_changelog \
+            "${{ github.event.pull_request.number }}" \
+            "${{ github.event.pull_request.title }}"
+      
+      - name: Check for changes
+        id: changes
+        run: |
+          if git diff --quiet docs/changelog.md; then
+            echo "changed=false" >> $GITHUB_OUTPUT
+          else
+            echo "changed=true" >> $GITHUB_OUTPUT
+          fi
+      
+      - name: Commit and push changes
+        if: steps.changes.outputs.changed == 'true'
+        run: |
+          git config --local user.email "action@github.com"
+          git config --local user.name "GitHub Action"
+          git add docs/changelog.md
+          git commit -m "Add changelog entry for PR #${{ github.event.pull_request.number }}"
+          git push
\ No newline at end of file
diff --git a/.github/workflows/version.yml b/.github/workflows/version.yml
index 2fda944c..7ab0ae62 100644
--- a/.github/workflows/version.yml
+++ b/.github/workflows/version.yml
@@ -39,7 +39,7 @@ jobs:
       - run: |
           git config user.name github-actions[bot]
           git config user.email 41898282+github-actions[bot]@users.noreply.github.com
-          VERSION=$(python increment_version.py $TYPE)
+          VERSION=$(python modify_changelog.py bump_version $TYPE)
           git checkout -b "version-$VERSION"
           git commit -am "Version $VERSION"
           git push -u origin HEAD
diff --git a/docs/changelog.md b/docs/changelog.md
index ddb82166..1792f2a9 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -4,6 +4,7 @@ _This project uses semantic versioning_
 
 ## UNRELEASED
 
+- Automatically Create Changelog Entry for PRs [#313](https://github.com/egraphs-good/egglog-python/pull/313)
 - Upgrade egglog which includes new backend.
   - Fixes implementation of the Python Object sort to work with objects with dupliating hashes but the same value.
     Also changes the representation to be an index into a list instead of the ID, making egglog programs more deterministic.
diff --git a/docs/reference/contributing.md b/docs/reference/contributing.md
index 8108fbc0..11556759 100644
--- a/docs/reference/contributing.md
+++ b/docs/reference/contributing.md
@@ -84,6 +84,10 @@ or bug fixes.
 
 When you are ready to submit your changes, please open a pull request. The CI will run the tests and check the code style.
 
+#### Changelog Automation
+
+When you open a pull request, a GitHub Action automatically adds an entry to the UNRELEASED section of the changelog using your PR title and number. This ensures the changelog stays up-to-date without manual intervention.
+
 ## Documentation
 
 We use the [Diátaxis framework](https://diataxis.fr/) to organize our documentation. The "explanation" section has
diff --git a/increment_version.py b/increment_version.py
deleted file mode 100644
index ce722c7b..00000000
--- a/increment_version.py
+++ /dev/null
@@ -1,79 +0,0 @@
-"""
-Version Bumper for Cargo.toml and Changelog.md
-
-This script automates the process of version bumping for Rust projects managed with Cargo. It reads the version
-from the cargo.toml file, increments it based on the specified component (major, minor, or patch), and updates
-both the cargo.toml and changelog.md files accordingly.
-
-It will also print out the new version number.
-
-Usage:
-    Run the script from the command line, specifying the type of version increment as an argument:
-    $ python bump_version.py [major|minor|patch]
-
-Arguments:
----------
-    major - Increments the major component of the version, sets minor and patch to 0
-    minor - Increments the minor component of the version, sets patch to 0
-    patch - Increments the patch component of the version
-
-From https://chat.openai.com/share/6b08906d-23a3-4193-9f4e-87076ce56ddb
-
-
-"""
-
-import datetime
-import re
-import sys
-from pathlib import Path
-
-
-def bump_version(major: int, minor: int, patch: int, part: str) -> str:
-    if part == "major":
-        major += 1
-        minor = 0
-        patch = 0
-    elif part == "minor":
-        minor += 1
-        patch = 0
-    elif part == "patch":
-        patch += 1
-    return f"{major}.{minor}.{patch}"
-
-
-def update_cargo_toml(file_path: Path, new_version: str) -> None:
-    content = file_path.read_text()
-    content = re.sub(r'version = "(\d+\.\d+\.\d+)"', f'version = "{new_version}"', content, count=1)
-    file_path.write_text(content)
-
-
-def update_changelog(file_path: Path, new_version: str) -> None:
-    today = datetime.datetime.now(tz=datetime.timezone.utc).strftime("%Y-%m-%d")
-    content = file_path.read_text()
-    new_section = f"## UNRELEASED\n\n## {new_version} ({today})"
-    content = content.replace("## UNRELEASED", new_section, 1)
-    file_path.write_text(content)
-
-
-if __name__ == "__main__":
-    if len(sys.argv) != 2 or sys.argv[1] not in ("major", "minor", "patch"):
-        print("Usage: python bump_version.py [major|minor|patch]")
-        sys.exit(1)
-
-    part = sys.argv[1]
-    cargo_path = Path("Cargo.toml")
-    changelog_path = Path("docs/changelog.md")
-
-    cargo_content = cargo_path.read_text()
-    version_match = re.search(r'version = "(\d+)\.(\d+)\.(\d+)"', cargo_content)
-    if version_match:
-        major, minor, patch = map(int, version_match.groups())
-    else:
-        print("Current version not found in cargo.toml.")
-        sys.exit(1)
-
-    new_version = bump_version(major, minor, patch, part)
-    old_version = f"{major}.{minor}.{patch}"
-    update_cargo_toml(cargo_path, new_version)
-    update_changelog(changelog_path, new_version)
-    print(new_version)
diff --git a/modify_changelog.py b/modify_changelog.py
new file mode 100644
index 00000000..2cdaa959
--- /dev/null
+++ b/modify_changelog.py
@@ -0,0 +1,208 @@
+"""
+Changelog Modifier and Version Bumper for Cargo.toml and Changelog.md
+
+This script automates the process of version bumping and changelog updates for Rust projects managed with Cargo.
+It reads the version from the cargo.toml file, increments it based on the specified component (major, minor, or patch),
+and updates both the cargo.toml and changelog.md files accordingly.
+
+It can also add PR entries to the UNRELEASED section of the changelog.
+
+Usage:
+    Version bumping:
+    $ python modify_changelog.py bump_version [major|minor|patch]
+
+    Adding PR entry:
+    $ python modify_changelog.py update_changelog <number> <title>
+
+Subcommands:
+-----------
+    bump_version - Increments version and updates changelog
+        major - Increments the major component of the version, sets minor and patch to 0
+        minor - Increments the minor component of the version, sets patch to 0
+        patch - Increments the patch component of the version
+
+    update_changelog - Add a PR entry to the UNRELEASED section
+        number - PR number
+        title - PR title
+
+From https://chat.openai.com/share/6b08906d-23a3-4193-9f4e-87076ce56ddb
+
+"""
+
+import argparse
+import datetime
+import re
+import sys
+from pathlib import Path
+
+
+def bump_version(major: int, minor: int, patch: int, part: str) -> str:
+    if part == "major":
+        major += 1
+        minor = 0
+        patch = 0
+    elif part == "minor":
+        minor += 1
+        patch = 0
+    elif part == "patch":
+        patch += 1
+    return f"{major}.{minor}.{patch}"
+
+
+def update_cargo_toml(file_path: Path, new_version: str) -> None:
+    content = file_path.read_text()
+    content = re.sub(r'version = "(\d+\.\d+\.\d+)"', f'version = "{new_version}"', content, count=1)
+    file_path.write_text(content)
+
+
+def find_unreleased_section(lines):
+    """Find the line number where UNRELEASED section starts and ends."""
+    unreleased_start = None
+    content_start = None
+
+    for i, line in enumerate(lines):
+        if line.strip() == "## UNRELEASED":
+            unreleased_start = i
+            continue
+
+        if unreleased_start is not None and content_start is None:
+            # Skip empty lines after ## UNRELEASED
+            if line.strip() == "":
+                continue
+            content_start = i
+            break
+
+    return unreleased_start, content_start
+
+
+def update_changelog_version(file_path: Path, new_version: str) -> None:
+    """Update changelog for version bump - replaces UNRELEASED with versioned section."""
+    today = datetime.datetime.now(tz=datetime.timezone.utc).strftime("%Y-%m-%d")
+    content = file_path.read_text()
+    new_section = f"## UNRELEASED\n\n## {new_version} ({today})"
+    content = content.replace("## UNRELEASED", new_section, 1)
+    file_path.write_text(content)
+
+
+def update_changelog_pr(file_path: Path, pr_number: str, pr_title: str, pr_url: str) -> bool:
+    """Update the changelog with the new PR entry. If entry exists, update it; otherwise add new entry."""
+    # Read the current changelog
+    with open(file_path, encoding="utf-8") as f:
+        lines = f.readlines()
+
+    # Find the UNRELEASED section
+    unreleased_start, content_start = find_unreleased_section(lines)
+
+    if unreleased_start is None:
+        print("ERROR: Could not find '## UNRELEASED' section in changelog")
+        return False
+
+    if content_start is None:
+        print("ERROR: Could not find content start after UNRELEASED section")
+        return False
+
+    # Create the new entry
+    new_entry = f"- {pr_title} [#{pr_number}]({pr_url})\n"
+
+    # Check if this PR entry already exists and update it if so
+    existing_entry_index = None
+    for i, line in enumerate(lines[content_start:], start=content_start):
+        if f"[#{pr_number}]" in line:
+            existing_entry_index = i
+            break
+        # Stop checking when we reach the next section
+        if line.startswith("## ") and line.strip() != "## UNRELEASED":
+            break
+
+    if existing_entry_index is not None:
+        # Update existing entry
+        lines[existing_entry_index] = new_entry
+        print(f"Updated changelog entry for PR #{pr_number}: {pr_title}")
+    else:
+        # Insert the new entry at the beginning of the unreleased content
+        lines.insert(content_start, new_entry)
+        print(f"Added changelog entry for PR #{pr_number}: {pr_title}")
+
+    # Write the updated changelog
+    with open(file_path, "w", encoding="utf-8") as f:
+        f.writelines(lines)
+
+    return True
+
+
+def handle_bump_version(args):
+    """Handle version bump subcommand."""
+    part = args.bump_type
+    cargo_path = Path("Cargo.toml")
+    changelog_path = Path("docs/changelog.md")
+
+    if not cargo_path.exists():
+        print("ERROR: Cargo.toml not found.")
+        sys.exit(1)
+
+    if not changelog_path.exists():
+        print("ERROR: Changelog file not found.")
+        sys.exit(1)
+
+    cargo_content = cargo_path.read_text()
+    version_match = re.search(r'version = "(\d+)\.(\d+)\.(\d+)"', cargo_content)
+    if version_match:
+        major, minor, patch = map(int, version_match.groups())
+    else:
+        print("Current version not found in cargo.toml.")
+        sys.exit(1)
+
+    new_version = bump_version(major, minor, patch, part)
+    update_cargo_toml(cargo_path, new_version)
+    update_changelog_version(changelog_path, new_version)
+    print(new_version)
+
+
+def handle_update_changelog(args):
+    """Handle update changelog subcommand."""
+    pr_number = args.number
+    pr_title = args.title
+
+    # Construct PR URL from repository info and PR number
+    # Default to the egglog-python repository
+    pr_url = f"https://github.com/egraphs-good/egglog-python/pull/{pr_number}"
+
+    changelog_path = Path(getattr(args, "changelog_path", "docs/changelog.md"))
+
+    if not changelog_path.exists():
+        print(f"ERROR: Changelog file not found: {changelog_path}")
+        sys.exit(1)
+
+    success = update_changelog_pr(changelog_path, pr_number, pr_title, pr_url)
+    if not success:
+        sys.exit(1)
+
+
+def main():
+    parser = argparse.ArgumentParser(description="Changelog modifier and version bumper")
+    subparsers = parser.add_subparsers(dest="command", help="Available commands")
+
+    # Bump version subcommand
+    bump_parser = subparsers.add_parser("bump_version", help="Bump version and update changelog")
+    bump_parser.add_argument("bump_type", choices=["major", "minor", "patch"], help="Type of version bump")
+
+    # Update changelog subcommand
+    changelog_parser = subparsers.add_parser("update_changelog", help="Add PR entry to changelog")
+    changelog_parser.add_argument("number", help="Pull request number")
+    changelog_parser.add_argument("title", help="Pull request title")
+    changelog_parser.add_argument("--changelog-path", default="docs/changelog.md", help="Path to changelog file")
+
+    args = parser.parse_args()
+
+    if not args.command:
+        parser.print_help()
+        sys.exit(1)
+
+    if args.command == "bump_version":
+        handle_bump_version(args)
+    elif args.command == "update_changelog":
+        handle_update_changelog(args)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/python/tests/test_modify_changelog.py b/python/tests/test_modify_changelog.py
new file mode 100644
index 00000000..7682e829
--- /dev/null
+++ b/python/tests/test_modify_changelog.py
@@ -0,0 +1,297 @@
+"""Tests for modify_changelog.py script."""
+
+import subprocess
+import sys
+import tempfile
+from pathlib import Path
+
+import pytest
+
+
+def test_modify_changelog_help():
+    """Test that the script shows help correctly."""
+    result = subprocess.run(
+        [sys.executable, "modify_changelog.py", "--help"],
+        capture_output=True,
+        text=True,
+        cwd=Path(__file__).parent.parent.parent,
+        check=False,
+    )
+    assert result.returncode == 0
+    assert "Changelog modifier and version bumper" in result.stdout
+    assert "bump_version" in result.stdout
+    assert "update_changelog" in result.stdout
+
+
+def test_bump_version_subcommand_help():
+    """Test that bump_version subcommand shows help correctly."""
+    result = subprocess.run(
+        [sys.executable, "modify_changelog.py", "bump_version", "--help"],
+        capture_output=True,
+        text=True,
+        cwd=Path(__file__).parent.parent.parent,
+        check=False,
+    )
+    assert result.returncode == 0
+    assert "Type of version bump" in result.stdout
+    assert "major" in result.stdout
+    assert "minor" in result.stdout
+    assert "patch" in result.stdout
+
+
+def test_update_changelog_subcommand_help():
+    """Test that update_changelog subcommand shows help correctly."""
+    result = subprocess.run(
+        [sys.executable, "modify_changelog.py", "update_changelog", "--help"],
+        capture_output=True,
+        text=True,
+        cwd=Path(__file__).parent.parent.parent,
+        check=False,
+    )
+    assert result.returncode == 0
+    assert "Pull request number" in result.stdout
+    assert "Pull request title" in result.stdout
+
+
+@pytest.mark.parametrize(
+    ("start_version", "bump_type", "expected_version"),
+    [
+        pytest.param("1.2.3", "patch", "1.2.4", id="patch_bump"),
+        pytest.param("1.2.3", "minor", "1.3.0", id="minor_bump"),
+        pytest.param("1.2.3", "major", "2.0.0", id="major_bump"),
+    ],
+)
+def test_bump_version(start_version, bump_type, expected_version):
+    """Test version bumping with different increment types."""
+    with tempfile.TemporaryDirectory() as temp_dir:
+        temp_path = Path(temp_dir)
+
+        # Create mock Cargo.toml
+        cargo_content = f'''[package]
+name = "test-package"
+version = "{start_version}"
+edition = "2021"
+'''
+        cargo_path = temp_path / "Cargo.toml"
+        cargo_path.write_text(cargo_content)
+
+        # Create mock changelog
+        changelog_content = f"""# Changelog
+
+## UNRELEASED
+
+## {start_version} (2024-01-01)
+
+- Some old change
+"""
+        docs_dir = temp_path / "docs"
+        docs_dir.mkdir()
+        changelog_path = docs_dir / "changelog.md"
+        changelog_path.write_text(changelog_content)
+
+        # Run the script
+        result = subprocess.run(
+            [
+                sys.executable,
+                str(Path(__file__).parent.parent.parent / "modify_changelog.py"),
+                "bump_version",
+                bump_type,
+            ],
+            capture_output=True,
+            text=True,
+            cwd=temp_path,
+            check=False,
+        )
+
+        assert result.returncode == 0
+        assert result.stdout.strip() == expected_version
+
+        # Check Cargo.toml was updated
+        updated_cargo = cargo_path.read_text()
+        assert f'version = "{expected_version}"' in updated_cargo
+
+        # Check changelog was updated
+        updated_changelog = changelog_path.read_text()
+        assert "## UNRELEASED" in updated_changelog
+        assert f"## {expected_version} (" in updated_changelog
+
+
+def test_update_changelog_new_entry():
+    """Test adding a new PR entry to changelog."""
+    with tempfile.TemporaryDirectory() as temp_dir:
+        temp_path = Path(temp_dir)
+
+        # Create mock changelog
+        changelog_content = """# Changelog
+
+## UNRELEASED
+
+## 1.2.3 (2024-01-01)
+
+- Some old change
+"""
+        docs_dir = temp_path / "docs"
+        docs_dir.mkdir()
+        changelog_path = docs_dir / "changelog.md"
+        changelog_path.write_text(changelog_content)
+
+        # Run the script
+        result = subprocess.run(
+            [
+                sys.executable,
+                str(Path(__file__).parent.parent.parent / "modify_changelog.py"),
+                "update_changelog",
+                "123",
+                "Fix important bug",
+            ],
+            capture_output=True,
+            text=True,
+            cwd=temp_path,
+            check=False,
+        )
+
+        assert result.returncode == 0
+        assert "Added changelog entry for PR #123: Fix important bug" in result.stdout
+
+        # Check changelog was updated
+        updated_changelog = changelog_path.read_text()
+        assert "- Fix important bug [#123](https://github.com/egraphs-good/egglog-python/pull/123)" in updated_changelog
+
+
+def test_update_changelog_duplicate_entry():
+    """Test that modifying PR title updates the existing changelog entry instead of making a new one."""
+    with tempfile.TemporaryDirectory() as temp_dir:
+        temp_path = Path(temp_dir)
+
+        # Create mock changelog with existing entry
+        changelog_content = """# Changelog
+
+## UNRELEASED
+
+- Fix important bug [#123](https://github.com/egraphs-good/egglog-python/pull/123)
+
+## 1.2.3 (2024-01-01)
+
+- Some old change
+"""
+        docs_dir = temp_path / "docs"
+        docs_dir.mkdir()
+        changelog_path = docs_dir / "changelog.md"
+        changelog_path.write_text(changelog_content)
+
+        # Run the script with updated title for same PR
+        result = subprocess.run(
+            [
+                sys.executable,
+                str(Path(__file__).parent.parent.parent / "modify_changelog.py"),
+                "update_changelog",
+                "123",
+                "Fix critical security bug",
+            ],
+            capture_output=True,
+            text=True,
+            cwd=temp_path,
+            check=False,
+        )
+
+        assert result.returncode == 0
+        assert "Updated changelog entry for PR #123: Fix critical security bug" in result.stdout
+
+        # Check that the changelog was updated, not duplicated
+        updated_changelog = changelog_path.read_text()
+        assert (
+            "- Fix critical security bug [#123](https://github.com/egraphs-good/egglog-python/pull/123)"
+            in updated_changelog
+        )
+        assert "- Fix important bug [#123]" not in updated_changelog  # Old entry should be gone
+        assert updated_changelog.count("[#123]") == 1  # Should only have one entry for PR 123
+
+
+def test_update_changelog_missing_file():
+    """Test error handling when changelog file is missing."""
+    with tempfile.TemporaryDirectory() as temp_dir:
+        temp_path = Path(temp_dir)
+
+        # Run the script without creating changelog file
+        result = subprocess.run(
+            [
+                sys.executable,
+                str(Path(__file__).parent.parent.parent / "modify_changelog.py"),
+                "update_changelog",
+                "123",
+                "Fix important bug",
+            ],
+            capture_output=True,
+            text=True,
+            cwd=temp_path,
+            check=False,
+        )
+
+        assert result.returncode == 1
+        assert "ERROR: Changelog file not found" in result.stdout
+
+
+def test_bump_version_missing_cargo():
+    """Test error handling when Cargo.toml file is missing."""
+    with tempfile.TemporaryDirectory() as temp_dir:
+        temp_path = Path(temp_dir)
+
+        # Create changelog but no Cargo.toml
+        docs_dir = temp_path / "docs"
+        docs_dir.mkdir()
+        changelog_path = docs_dir / "changelog.md"
+        changelog_path.write_text("# Changelog\n\n## UNRELEASED\n")
+
+        # Run the script
+        result = subprocess.run(
+            [sys.executable, str(Path(__file__).parent.parent.parent / "modify_changelog.py"), "bump_version", "patch"],
+            capture_output=True,
+            text=True,
+            cwd=temp_path,
+            check=False,
+        )
+
+        assert result.returncode == 1
+        assert "ERROR: Cargo.toml not found" in result.stdout
+
+
+def test_custom_changelog_path():
+    """Test using custom changelog path."""
+    with tempfile.TemporaryDirectory() as temp_dir:
+        temp_path = Path(temp_dir)
+
+        # Create mock changelog in custom location
+        changelog_content = """# Changelog
+
+## UNRELEASED
+
+## 1.2.3 (2024-01-01)
+
+- Some old change
+"""
+        custom_changelog_path = temp_path / "CHANGELOG.md"
+        custom_changelog_path.write_text(changelog_content)
+
+        # Run the script with custom path
+        result = subprocess.run(
+            [
+                sys.executable,
+                str(Path(__file__).parent.parent.parent / "modify_changelog.py"),
+                "update_changelog",
+                "456",
+                "Add new feature",
+                "--changelog-path",
+                "CHANGELOG.md",
+            ],
+            capture_output=True,
+            text=True,
+            cwd=temp_path,
+            check=False,
+        )
+
+        assert result.returncode == 0
+        assert "Added changelog entry for PR #456: Add new feature" in result.stdout
+
+        # Check changelog was updated
+        updated_changelog = custom_changelog_path.read_text()
+        assert "- Add new feature [#456](https://github.com/egraphs-good/egglog-python/pull/456)" in updated_changelog