diff --git a/README.md b/README.md
index 9d0e675..54181ef 100644
--- a/README.md
+++ b/README.md
@@ -2,6 +2,82 @@
 
 Set of reusable workflows used by Onfido Github actions.
 
+## Lock
+
+A distributed lock mechanism to prevent parallel execution of integration tests across repositories. Uses a git branch in a dedicated lock repository (`onfido/ci-lock`) as an atomic mutex.
+
+### How it works
+
+- Lock branch **does not exist** = lock is **free**
+- Lock branch **exists** = lock is **taken**
+
+The `lock/acquire` action attempts to create a branch (e.g., `locks/client-libraries-integration-tests`) in the lock repository. Git ref creation is atomic — only one process can succeed. If it fails, the action polls until the branch is deleted (lock released) or times out.
+
+The `lock/release` action deletes the lock branch, making the lock available again.
+
+### Setup
+
+1. Create the lock repository (e.g., `onfido/ci-lock`) with at least a `main` branch
+2. Create a GitHub App with write access to the lock repository
+3. Install the app on the org and grant it access to the `ci-lock` repo
+4. Store `ONFIDO_CI_LOCK_APP_ID` and `ONFIDO_CI_LOCK_PRIVATE_KEY` as org-level secrets
+
+### Usage
+
+```yaml
+jobs:
+  integration-tests:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: onfido/onfido-actions/lock/acquire@main
+        with:
+          app-id: ${{ secrets.ONFIDO_CI_LOCK_APP_ID }}
+          app-private-key: ${{ secrets.ONFIDO_CI_LOCK_PRIVATE_KEY }}
+          lock-name: "client-libraries-integration-tests"  # optional, this is the default
+          timeout: "1800"                                  # optional, default 30 min
+          poll-interval: "30"                              # optional, default 30s
+
+      # ... run your integration tests ...
+
+      - uses: onfido/onfido-actions/lock/release@main
+        if: always()
+        with:
+          app-id: ${{ secrets.ONFIDO_CI_LOCK_APP_ID }}
+          app-private-key: ${{ secrets.ONFIDO_CI_LOCK_PRIVATE_KEY }}
+          lock-name: "client-libraries-integration-tests"
+```
+
+### Inputs
+
+#### `lock/acquire`
+
+| Input | Required | Default | Description |
+|-------|----------|---------|-------------|
+| `app-id` | yes | | GitHub App ID |
+| `app-private-key` | yes | | GitHub App private key |
+| `lock-name` | yes | `client-libraries-integration-tests` | Lock name (becomes branch `locks/<name>`) |
+| `lock-repo` | no | `onfido/ci-lock` | Repository used for locking |
+| `timeout` | no | `1800` | Max wait time in seconds |
+| `poll-interval` | no | `30` | Seconds between retries |
+
+#### `lock/release`
+
+| Input | Required | Default | Description |
+|-------|----------|---------|-------------|
+| `app-id` | yes | | GitHub App ID |
+| `app-private-key` | yes | | GitHub App private key |
+| `lock-name` | yes | `client-libraries-integration-tests` | Lock name (must match acquire) |
+| `lock-repo` | no | `onfido/ci-lock` | Repository used for locking |
+
+### Stale lock recovery
+
+If a workflow crashes without releasing the lock, manually delete the branch:
+```bash
+gh api repos/onfido/ci-lock/git/refs/heads/locks/client-libraries-integration-tests -X DELETE
+```
+
+> **Important:** Always use `if: always()` on the release step to ensure the lock is freed even if tests fail.
+
 ## Changelog update
 
 To manually update changelog, run:
@@ -11,4 +87,4 @@ RELEASE_BODY="
   - Nested changelog line from spec change
 - Extra changelog line from library change
 " ../onfido-action/update-changelog/update-changelog.sh
-```
\ No newline at end of file
+```
diff --git a/lock/acquire/action.yml b/lock/acquire/action.yml
new file mode 100644
index 0000000..a81eb61
--- /dev/null
+++ b/lock/acquire/action.yml
@@ -0,0 +1,125 @@
+name: Acquire Lock
+description: |
+  Acquire a distributed lock using a git branch in a shared repository.
+  Attempts to create a lock branch — if it succeeds, the lock is acquired.
+  If the branch already exists (lock held), polls until it's released or times out.
+
+inputs:
+  app-id:
+    description: "GitHub App ID for generating a token"
+    required: true
+  app-private-key:
+    description: "GitHub App private key for generating a token"
+    required: true
+  lock-name:
+    description: "Name of the lock (used as branch name under locks/ prefix)"
+    required: true
+    default: "client-libraries-integration-tests"
+  lock-repo:
+    description: "Repository used for locking (owner/repo format)"
+    required: false
+    default: "onfido/ci-lock"
+  timeout:
+    description: "Maximum time in seconds to wait for the lock (default: 1800 = 30 min)"
+    required: false
+    default: "1800"
+  poll-interval:
+    description: "Seconds between lock acquisition attempts (default: 30)"
+    required: false
+    default: "30"
+
+outputs:
+  acquired:
+    description: "Whether the lock was successfully acquired"
+    value: ${{ steps.acquire.outputs.acquired }}
+  lock-branch:
+    description: "The branch name used for this lock"
+    value: ${{ steps.acquire.outputs.lock_branch }}
+
+runs:
+  using: "composite"
+  steps:
+    - name: Generate token from GitHub App
+      id: app-token
+      uses: actions/create-github-app-token@v2
+      with:
+        app-id: ${{ inputs.app-id }}
+        private-key: ${{ inputs.app-private-key }}
+        owner: ${{ github.repository_owner }}
+        repositories: ci-lock
+
+    - name: Acquire lock
+      id: acquire
+      shell: bash
+      env:
+        GH_TOKEN: ${{ steps.app-token.outputs.token }}
+        LOCK_NAME: ${{ inputs.lock-name }}
+        LOCK_REPO: ${{ inputs.lock-repo }}
+        TIMEOUT: ${{ inputs.timeout }}
+        POLL_INTERVAL: ${{ inputs.poll-interval }}
+      run: |
+        LOCK_BRANCH="locks/${LOCK_NAME}"
+        echo "lock_branch=${LOCK_BRANCH}" >> "$GITHUB_OUTPUT"
+
+        elapsed=0
+
+        # Get the default branch SHA to use as base for the lock branch
+        get_base_sha() {
+          gh api "repos/${LOCK_REPO}/git/ref/heads/main" --jq '.object.sha' 2>/dev/null || \
+          gh api "repos/${LOCK_REPO}/git/ref/heads/master" --jq '.object.sha' 2>/dev/null
+        }
+
+        # Try to create the lock branch (atomic operation)
+        try_acquire() {
+          local base_sha
+          base_sha=$(get_base_sha)
+
+          if [ -z "$base_sha" ]; then
+            echo "::error::Could not find base branch in ${LOCK_REPO}"
+            exit 1
+          fi
+
+          # Creating a ref is atomic — only one process can succeed
+          local result
+          result=$(gh api "repos/${LOCK_REPO}/git/refs" \
+            -X POST \
+            -f "ref=refs/heads/${LOCK_BRANCH}" \
+            -f "sha=${base_sha}" 2>&1) && return 0 || return 1
+        }
+
+        echo "Attempting to acquire lock '${LOCK_NAME}' (branch: ${LOCK_BRANCH} in ${LOCK_REPO})..."
+
+        while [ $elapsed -lt $TIMEOUT ]; do
+          if try_acquire; then
+            echo "✅ Lock '${LOCK_NAME}' acquired successfully"
+            echo "acquired=true" >> "$GITHUB_OUTPUT"
+
+            # Update the lock branch with a commit containing metadata
+            LOCK_INFO="Lock acquired by ${GITHUB_REPOSITORY} - ${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}/actions/runs/${GITHUB_RUN_ID}"
+            TMPDIR=$(mktemp -d)
+            git clone --depth 1 --branch "${LOCK_BRANCH}" "https://x-access-token:${GH_TOKEN}@github.com/${LOCK_REPO}.git" "$TMPDIR" 2>/dev/null || true
+            if [ -d "$TMPDIR/.git" ]; then
+              cd "$TMPDIR"
+              git config user.name "github-actions[bot]"
+              git config user.email "github-actions[bot]@users.noreply.github.com"
+              git commit --allow-empty -m "$LOCK_INFO"
+              git push origin "${LOCK_BRANCH}" 2>/dev/null || true
+              cd - > /dev/null
+            fi
+            rm -rf "$TMPDIR"
+
+            exit 0
+          fi
+
+          # Show who currently holds the lock
+          HOLDER=$(gh api "repos/${LOCK_REPO}/commits/${LOCK_BRANCH}" --jq '.commit.message' 2>/dev/null || echo "unknown")
+          echo "⏳ Lock '${LOCK_NAME}' is held (${elapsed}/${TIMEOUT}s elapsed, retrying in ${POLL_INTERVAL}s)"
+          echo "   Holder: ${HOLDER}"
+          sleep "$POLL_INTERVAL"
+          elapsed=$((elapsed + POLL_INTERVAL))
+        done
+
+        echo "❌ Timed out waiting for lock '${LOCK_NAME}' after ${TIMEOUT}s"
+        echo "acquired=false" >> "$GITHUB_OUTPUT"
+        echo "::error::Timed out waiting for lock '${LOCK_NAME}' after ${TIMEOUT}s"
+        exit 1
diff --git a/lock/release/action.yml b/lock/release/action.yml
new file mode 100644
index 0000000..c1127f9
--- /dev/null
+++ b/lock/release/action.yml
@@ -0,0 +1,57 @@
+name: Release Lock
+description: |
+  Release a distributed lock by deleting the lock branch from the shared repository.
+  Should always be called with `if: always()` to ensure the lock is released even on failure.
+
+inputs:
+  app-id:
+    description: "GitHub App ID for generating a token"
+    required: true
+  app-private-key:
+    description: "GitHub App private key for generating a token"
+    required: true
+  lock-name:
+    description: "Name of the lock (used as branch name under locks/ prefix)"
+    required: true
+    default: "client-libraries-integration-tests"
+  lock-repo:
+    description: "Repository used for locking (owner/repo format)"
+    required: false
+    default: "onfido/ci-lock"
+
+runs:
+  using: "composite"
+  steps:
+    - name: Generate token from GitHub App
+      id: app-token
+      uses: actions/create-github-app-token@v2
+      with:
+        app-id: ${{ inputs.app-id }}
+        private-key: ${{ inputs.app-private-key }}
+        owner: ${{ github.repository_owner }}
+        repositories: ci-lock
+
+    - name: Release lock
+      shell: bash
+      env:
+        GH_TOKEN: ${{ steps.app-token.outputs.token }}
+        LOCK_NAME: ${{ inputs.lock-name }}
+        LOCK_REPO: ${{ inputs.lock-repo }}
+      run: |
+        LOCK_BRANCH="locks/${LOCK_NAME}"
+
+        echo "Releasing lock '${LOCK_NAME}' (deleting branch: ${LOCK_BRANCH} in ${LOCK_REPO})..."
+
+        # Verify we own the lock before releasing it
+        LOCK_MSG=$(gh api "repos/${LOCK_REPO}/commits/${LOCK_BRANCH}" --jq '.commit.message' 2>/dev/null || echo "")
+        if [ -n "$LOCK_MSG" ] && ! echo "$LOCK_MSG" | grep -q "${GITHUB_RUN_ID}"; then
+          echo "⚠️  Lock is held by another run: ${LOCK_MSG}"
+          echo "⚠️  Skipping release to avoid breaking another workflow's lock"
+          exit 0
+        fi
+
+        if gh api "repos/${LOCK_REPO}/git/refs/heads/${LOCK_BRANCH}" -X DELETE 2>/dev/null; then
+          echo "✅ Lock '${LOCK_NAME}' released successfully"
+        else
+          echo "⚠️  Lock branch not found — may have already been released"
+        fi
diff --git a/should-run-integration-tests/action.yml b/should-run-integration-tests/action.yml
new file mode 100644
index 0000000..cb69950
--- /dev/null
+++ b/should-run-integration-tests/action.yml
@@ -0,0 +1,59 @@
+name: Should Run Integration Tests
+description: |
+  Determines whether integration tests should run based on the workflow event.
+  Returns result=true for:
+  - pull_request: only if NOT from a fork (forks don't have access to secrets)
+  - push: only if it's a merge from a fork PR (to catch what couldn't run pre-merge)
+  - release, workflow_dispatch, schedule: always
+
+inputs:
+  github-token:
+    description: "GitHub token for API access (typically github.token)"
+    required: false
+    default: ${{ github.token }}
+
+outputs:
+  result:
+    description: "'true' if integration tests should run, empty otherwise"
+    value: ${{ steps.check.outputs.result }}
+
+runs:
+  using: "composite"
+  steps:
+    - name: Check if integration tests should run
+      id: check
+      shell: bash
+      env:
+        GH_TOKEN: ${{ inputs.github-token }}
+        EVENT_NAME: ${{ github.event_name }}
+        PR_HEAD_REPO_FULL_NAME: ${{ github.event.pull_request.head.repo.full_name }}
+        REPO: ${{ github.repository }}
+        REPO_OWNER: ${{ github.repository_owner }}
+        SHA: ${{ github.sha }}
+      run: |
+        case "$EVENT_NAME" in
+          release|workflow_dispatch|schedule)
+            echo "result=true" >> "$GITHUB_OUTPUT"
+            ;;
+          pull_request)
+            # Skip fork PRs — secrets are not available
+            if [ "$PR_HEAD_REPO_FULL_NAME" = "$REPO" ]; then
+              echo "result=true" >> "$GITHUB_OUTPUT"
+            else
+              echo "Skipping: PR from fork ($PR_HEAD_REPO_FULL_NAME)"
+            fi
+            ;;
+          push)
+            # On push, only run tests if it's a merge from a fork PR
+            # (fork PRs can't run integration tests pre-merge due to missing secrets)
+            PR_OWNER=$(gh pr list --repo "$REPO" --state merged \
+              --search "$SHA" --json headRepositoryOwner \
+              --jq '.[0].headRepositoryOwner.login // empty' 2>/dev/null)
+            if [ -n "$PR_OWNER" ] && [ "$PR_OWNER" != "$REPO_OWNER" ]; then
+              echo "Push from fork PR (owner: $PR_OWNER) — running integration tests"
+              echo "result=true" >> "$GITHUB_OUTPUT"
+            else
+              echo "Skipping: push is not from a fork PR"
+            fi
+            ;;
+        esac