diff --git a/SECURITY_AUDIT.md b/SECURITY_AUDIT.md
index a7a4f91d..253a34fe 100644
--- a/SECURITY_AUDIT.md
+++ b/SECURITY_AUDIT.md
@@ -289,7 +289,14 @@ ftp = ftplib.FTP()  # nosec B321 - Plaintext FTP intentional when configured
   - Applied to `app/api/files.py` (file list sort + search query parameters)
   - Applied to `app/api/logs.py` (task_id query filter and path parameter)
   - 30 unit tests added in `tests/test_input_validation.py`
-- ⏳ **TODO:** Implement proper API key rotation mechanisms ([#168](https://github.com/christianlouis/DocuElevate/issues/168))
+- ✅ **COMPLETED:** Implement proper API key rotation mechanisms ([#168](https://github.com/christianlouis/DocuElevate/issues/168))
+  - `docs/CredentialRotationGuide.md` — comprehensive rotation guide covering:
+    - Recommended rotation schedule for all credential types
+    - Per-credential rotation procedures for OpenAI, Azure, AWS S3, Dropbox, Google Drive, OneDrive, Authentik, Paperless-ngx, SMTP, IMAP, Nextcloud, FTP, SFTP, WebDAV, and admin credentials
+    - Onboarding instructions (creating service-specific credentials with minimal permissions)
+    - Offboarding instructions (revocation, rotation of shared credentials, audit log review)
+    - Emergency revocation procedure
+  - `GET /api/settings/credentials` — admin-only endpoint listing all sensitive credential settings with configured/unconfigured status and source (`env` vs `db`), enabling credential rotation audits without exposing secret values
 
 ### Infrastructure Security
 - ✅ TrustedHostMiddleware configured (restricts valid hosts)
@@ -328,7 +335,7 @@ ftp = ftplib.FTP()  # nosec B321 - Plaintext FTP intentional when configured
 1. **Security training documentation** - For contributors
 2. **Penetration testing** - Professional security assessment
 3. **Bug bounty program** - Community security contributions
-4. **API key rotation** - Automated credential rotation ([#168](https://github.com/christianlouis/DocuElevate/issues/168))
+4. ~~**API key rotation**~~ ✅ Implemented — `docs/CredentialRotationGuide.md` documents rotation procedures, onboarding/offboarding, and emergency revocation; `GET /api/settings/credentials` provides a credential audit endpoint ([#168](https://github.com/christianlouis/DocuElevate/issues/168))
 
 ## Security Contact
 
diff --git a/app/api/settings.py b/app/api/settings.py
index 16155cb1..e5b92e7e 100644
--- a/app/api/settings.py
+++ b/app/api/settings.py
@@ -187,6 +187,60 @@ async def delete_setting(key: str, request: Request, db: DbSession, admin: Admin
         )
 
 
+@router.get("/credentials")
+async def list_credentials(request: Request, db: DbSession, admin: AdminUser):
+    """
+    List all sensitive credential settings with their configured/unconfigured status.
+
+    Returns a credential audit report indicating which credentials are set and whether
+    each value originates from the database or an environment variable.
+    This endpoint is intended to support credential rotation workflows.
+    Admin only.
+    """
+    try:
+        db_settings = get_all_settings_from_db(db)
+        credentials = []
+
+        for key, meta in SETTING_METADATA.items():
+            if not meta.get("sensitive", False):
+                continue
+
+            env_value = getattr(settings, key, None)
+            in_db = key in db_settings and db_settings[key]
+
+            if in_db:
+                source = "db"
+                configured = True
+            elif env_value:
+                source = "env"
+                configured = True
+            else:
+                source = None
+                configured = False
+
+            credentials.append(
+                {
+                    "key": key,
+                    "category": meta.get("category", "Other"),
+                    "description": meta.get("description", ""),
+                    "configured": configured,
+                    "source": source,
+                    "restart_required": meta.get("restart_required", False),
+                }
+            )
+
+        configured_count = sum(1 for c in credentials if c["configured"])
+        return {
+            "credentials": credentials,
+            "total": len(credentials),
+            "configured_count": configured_count,
+            "unconfigured_count": len(credentials) - configured_count,
+        }
+    except Exception as e:
+        logger.error(f"Error retrieving credential list: {e}")
+        raise HTTPException(status_code=status.HTTP_500_INTERNAL_SERVER_ERROR, detail="Failed to retrieve credentials")
+
+
 @router.post("/bulk-update")
 async def bulk_update_settings(updates: list[SettingUpdate], request: Request, db: DbSession, admin: AdminUser):
     """
diff --git a/docs/CredentialRotationGuide.md b/docs/CredentialRotationGuide.md
new file mode 100644
index 00000000..bb911752
--- /dev/null
+++ b/docs/CredentialRotationGuide.md
@@ -0,0 +1,260 @@
+# Credential Rotation Guide
+
+This guide documents how to rotate API keys and credentials used by DocuElevate, along with onboarding and offboarding procedures for team members and service accounts.
+
+## Overview
+
+DocuElevate integrates with several external services that require API keys, tokens, or passwords. Regularly rotating these credentials limits the blast radius of a potential leak and is a security best practice.
+
+Credentials fall into two categories:
+
+| Category | Examples |
+|---|---|
+| **API keys** | OpenAI API key, Azure AI key, Paperless-ngx API token, AWS access keys |
+| **OAuth tokens / secrets** | Dropbox, Google Drive, OneDrive, Authentik client secrets and refresh tokens |
+| **Passwords** | Admin password, Nextcloud, Email (SMTP), IMAP, FTP, SFTP, WebDAV |
+| **Private keys** | SFTP private key and passphrase |
+
+All credentials are stored either in environment variables or, when set via the Settings UI, encrypted in the database using Fernet symmetric encryption (keyed from `SESSION_SECRET`).
+
+---
+
+## Recommended Rotation Schedule
+
+| Credential Type | Recommended Rotation Interval |
+|---|---|
+| API keys (OpenAI, Azure, AWS, Paperless) | Every 90 days |
+| OAuth client secrets | Every 180 days |
+| OAuth refresh tokens | Rotate on revocation / after each re-authorization |
+| Passwords (SMTP, IMAP, FTP, SFTP, Nextcloud, WebDAV) | Every 90 days or on personnel change |
+| Admin password | Every 90 days or on personnel change |
+| `SESSION_SECRET` | On suspected compromise; note all active sessions will be invalidated |
+
+---
+
+## How to Rotate a Credential
+
+DocuElevate supports two rotation methods:
+
+### Method 1 — Settings API (recommended, zero-downtime)
+
+Use the Settings REST API to update individual credentials while the application is running. No restart is needed for most credentials (check `restart_required` in the response).
+
+```bash
+# Rotate the OpenAI API key
+curl -X POST https://<your-host>/api/settings/openai_api_key \
+  -H "Content-Type: application/json" \
+  -b "session=<admin-session-cookie>" \
+  -d '{"key": "openai_api_key", "value": "sk-new-key-here"}'
+```
+
+The endpoint returns `"restart_required": true` for settings that require an application restart to take effect (e.g., database URL, session secret). All AI-service and storage-provider credentials take effect immediately without a restart.
+
+### Method 2 — Environment variable / `.env` file
+
+1. Update the relevant variable in your `.env` file (or your container/Kubernetes secret).
+2. Restart the application so the new value is loaded:
+
+```bash
+docker compose restart api worker
+```
+
+> **Note:** Settings stored in the database take precedence over environment variables. If you previously set a credential via the Settings UI, you must also update or delete it from the database (via the Settings API) to have the environment variable take effect.
+
+---
+
+## Per-Credential Rotation Procedures
+
+### OpenAI API Key
+
+1. Log in to [platform.openai.com](https://platform.openai.com) → **API keys**.
+2. Create a new secret key and copy it.
+3. Update in DocuElevate:
+   ```
+   POST /api/settings/openai_api_key  {"key": "openai_api_key", "value": "<new-key>"}
+   ```
+4. Verify document processing still works (upload a test file).
+5. Delete the old key in the OpenAI dashboard.
+
+### Azure Document Intelligence Key
+
+1. Open [portal.azure.com](https://portal.azure.com) → your Document Intelligence resource → **Keys and Endpoint**.
+2. Regenerate **Key 2** while **Key 1** is still live (avoids downtime).
+3. Update `azure_ai_key` in DocuElevate with the new key.
+4. Verify connectivity, then regenerate **Key 1** and optionally update again.
+
+### AWS S3 Access Keys
+
+1. In the **IAM Console**, create a new access key for the service user.
+2. Update both `aws_access_key_id` and `aws_secret_access_key` in DocuElevate together (use the bulk-update endpoint or update both settings in sequence before verifying).
+3. Test an S3 upload from DocuElevate.
+4. Deactivate the old IAM access key, then delete it after 24 hours.
+
+### Dropbox App Credentials & Refresh Token
+
+Dropbox refresh tokens are long-lived; rotate them by re-authorizing the application:
+
+1. In [dropbox.com/developers](https://www.dropbox.com/developers), revoke the existing token.
+2. Follow the Dropbox OAuth flow documented in `docs/DropboxSetup.md` to obtain a new refresh token.
+3. Update `dropbox_refresh_token` (and `dropbox_app_key` / `dropbox_app_secret` if also rotating those).
+
+### Google Drive OAuth Credentials
+
+1. In the [Google Cloud Console](https://console.cloud.google.com), navigate to **APIs & Services → Credentials**.
+2. Rotate the OAuth client secret: delete the old secret and create a new one.
+3. Update `google_drive_client_secret` in DocuElevate.
+4. Re-authorize to obtain a fresh refresh token and update `google_drive_refresh_token`.
+
+For service-account credentials (`google_drive_credentials_json`):
+
+1. Create a new service-account key in the Google Cloud Console.
+2. Update `google_drive_credentials_json` with the new JSON.
+3. Verify access, then delete the old key.
+
+### OneDrive (Microsoft OAuth)
+
+1. In **Azure App Registrations**, navigate to **Certificates & secrets** for your app.
+2. Add a new client secret.
+3. Update `onedrive_client_secret` in DocuElevate.
+4. Re-authorize via the OAuth flow to get a fresh `onedrive_refresh_token`.
+5. Delete the old client secret in Azure.
+
+### Authentik (OIDC)
+
+1. In your Authentik admin panel, navigate to the DocuElevate application and regenerate the client secret.
+2. Update `authentik_client_secret` in DocuElevate.
+3. Restart the application (this setting requires a restart: `restart_required: true`).
+
+### Paperless-ngx API Token
+
+1. Log in to your Paperless-ngx instance → **Settings → API Tokens**.
+2. Create a new token.
+3. Update `paperless_ngx_api_token` in DocuElevate.
+4. Verify document routing works, then revoke the old token.
+
+### SMTP / Email Password
+
+1. Rotate the password in your mail server or email provider.
+2. Update `email_password` in DocuElevate.
+
+### IMAP Passwords
+
+Update `imap1_password` and/or `imap2_password` after rotating the credentials with your email provider.
+
+### Nextcloud Password / App Password
+
+1. In Nextcloud → **Settings → Security**, revoke the existing app password and create a new one.
+2. Update `nextcloud_password` in DocuElevate.
+
+### FTP / SFTP / WebDAV Passwords
+
+1. Rotate the credential on the respective server.
+2. Update `ftp_password`, `sftp_password`, or `webdav_password` in DocuElevate.
+
+### SFTP Private Key
+
+1. Generate a new key pair:
+   ```bash
+   ssh-keygen -t ed25519 -f ~/.ssh/docuelevate_sftp -C "docuelevate-sftp"
+   ```
+2. Install the new public key on the SFTP server.
+3. Update `sftp_private_key` (and `sftp_private_key_passphrase` if encrypted) in DocuElevate.
+4. Verify connectivity, then remove the old public key from the SFTP server.
+
+### Admin Password
+
+1. Update `admin_password` in DocuElevate (via the Settings UI or API).
+2. Communicate the new password to any users who share it (discouraged; prefer individual accounts via OAuth).
+3. Requires application restart.
+
+### `SESSION_SECRET`
+
+> **Warning:** Rotating `SESSION_SECRET` invalidates all active user sessions. All logged-in users will be signed out immediately.
+
+1. Generate a new secret (minimum 32 characters):
+   ```bash
+   python -c "import secrets; print(secrets.token_hex(32))"
+   ```
+2. Update the environment variable or `.env` file.
+3. Restart the application.
+4. Existing encrypted settings stored in the database **will no longer be readable** because the encryption key is derived from `SESSION_SECRET`. You must re-enter all sensitive settings that were stored via the UI after rotating this value.
+
+---
+
+## Bulk Credential Audit
+
+Use the dedicated endpoint to list all credential settings and their configured/unconfigured status:
+
+```bash
+GET /api/settings/credentials
+```
+
+Example response:
+
+```json
+{
+  "credentials": [
+    {
+      "key": "openai_api_key",
+      "category": "AI Services",
+      "description": "OpenAI API key for metadata extraction",
+      "configured": true,
+      "source": "env"
+    },
+    {
+      "key": "azure_ai_key",
+      "category": "AI Services",
+      "description": "Azure AI key for document intelligence",
+      "configured": true,
+      "source": "db"
+    },
+    ...
+  ],
+  "total": 24,
+  "configured_count": 8,
+  "unconfigured_count": 16
+}
+```
+
+The `source` field indicates whether the value comes from the **database** (`db`) or an **environment variable** (`env`).
+
+---
+
+## Onboarding a New Team Member or Service Account
+
+1. **Identify required credentials** – Use `GET /api/settings/credentials` to see which credentials are active in the deployment.
+2. **Create service-specific credentials** – For each external service (OpenAI, AWS, etc.) create a new API key or sub-account rather than sharing the existing one. This enables individual revocation without disrupting others.
+3. **Set credentials via the Settings API** – Provide the new credential via `POST /api/settings/{key}`. The value is encrypted at rest.
+4. **Restrict access** – Ensure the new service account has only the minimum permissions needed (e.g., an S3 IAM user with write access to the specific bucket only).
+5. **Document the credential** – Record *which* system generated the credential and *when* it was created, so it can be identified during offboarding.
+
+---
+
+## Offboarding a Team Member or Decommissioning a Service Account
+
+1. **Identify credentials tied to the departing user** – Review all third-party services for keys or OAuth authorizations issued under their account.
+2. **Revoke credentials** – Delete or disable the API key/token in each third-party service immediately.
+3. **Rotate shared credentials** – If any credential was shared (e.g., a team-wide admin password), rotate it now using the procedures above.
+4. **Update DocuElevate** – Set the new credential via `POST /api/settings/{key}` or delete the old entry via `DELETE /api/settings/{key}` if the service is no longer used.
+5. **Verify operations** – Trigger a test document processing run to confirm all integrations still work.
+6. **Audit logs** – Review audit logs for any anomalous activity by the departing user before revoking access.
+
+---
+
+## Emergency Credential Revocation
+
+If a credential is believed to be compromised:
+
+1. **Revoke immediately** in the external service (do not wait to have a replacement ready).
+2. **Review audit logs** for unauthorized usage.
+3. **Generate and deploy a replacement** credential as soon as possible.
+4. **Notify stakeholders** per your incident response plan (see [SECURITY.md](../SECURITY.md)).
+
+---
+
+## Related Documentation
+
+- [Configuration Guide](ConfigurationGuide.md) — Full list of environment variables
+- [Deployment Guide](DeploymentGuide.md) — Deployment and restart procedures
+- [SECURITY_AUDIT.md](../SECURITY_AUDIT.md) — Security audit findings and status
+- [SECURITY.md](../SECURITY.md) — Security contact and disclosure policy
diff --git a/tests/test_api_settings.py b/tests/test_api_settings.py
index b31e0d07..e61df569 100644
--- a/tests/test_api_settings.py
+++ b/tests/test_api_settings.py
@@ -203,3 +203,177 @@ class TestSettingModels:
         assert "test_key" in response.settings
         assert "General" in response.categories
         assert "test_key" in response.db_settings
+
+
+@pytest.mark.unit
+class TestListCredentials:
+    """Tests for the list_credentials function (GET /api/settings/credentials)."""
+
+    @patch("app.api.settings.get_all_settings_from_db")
+    def test_list_credentials_returns_sensitive_keys_only(self, mock_db_settings):
+        """Test that list_credentials only includes keys marked sensitive in SETTING_METADATA."""
+        import asyncio
+
+        from app.api.settings import list_credentials
+        from app.utils.settings_service import SETTING_METADATA
+
+        mock_db_settings.return_value = {}
+        mock_request = MagicMock()
+        mock_db = MagicMock()
+        mock_admin = {"is_admin": True}
+
+        with patch("app.api.settings.settings") as mock_settings:
+            for key in SETTING_METADATA:
+                setattr(mock_settings, key, None)
+
+            result = asyncio.get_event_loop().run_until_complete(
+                list_credentials(mock_request, mock_db, mock_admin)
+            )
+
+        returned_keys = {c["key"] for c in result["credentials"]}
+        sensitive_keys = {k for k, v in SETTING_METADATA.items() if v.get("sensitive")}
+        assert returned_keys == sensitive_keys
+
+    @patch("app.api.settings.get_all_settings_from_db")
+    def test_list_credentials_source_db_when_in_database(self, mock_db_settings):
+        """Test that credentials stored in the database report source='db'."""
+        import asyncio
+
+        from app.api.settings import list_credentials
+
+        mock_db_settings.return_value = {"openai_api_key": "sk-db-key"}
+        mock_request = MagicMock()
+        mock_db = MagicMock()
+        mock_admin = {"is_admin": True}
+
+        with patch("app.api.settings.settings") as mock_settings:
+            mock_settings.openai_api_key = "sk-env-key"
+
+            result = asyncio.get_event_loop().run_until_complete(
+                list_credentials(mock_request, mock_db, mock_admin)
+            )
+
+        openai_entry = next(c for c in result["credentials"] if c["key"] == "openai_api_key")
+        assert openai_entry["source"] == "db"
+        assert openai_entry["configured"] is True
+
+    @patch("app.api.settings.get_all_settings_from_db")
+    def test_list_credentials_source_env_when_only_in_env(self, mock_db_settings):
+        """Test that credentials only in env report source='env'."""
+        import asyncio
+
+        from app.api.settings import list_credentials
+
+        mock_db_settings.return_value = {}
+        mock_request = MagicMock()
+        mock_db = MagicMock()
+        mock_admin = {"is_admin": True}
+
+        with patch("app.api.settings.settings") as mock_settings:
+            mock_settings.openai_api_key = "sk-env-key"
+
+            result = asyncio.get_event_loop().run_until_complete(
+                list_credentials(mock_request, mock_db, mock_admin)
+            )
+
+        openai_entry = next(c for c in result["credentials"] if c["key"] == "openai_api_key")
+        assert openai_entry["source"] == "env"
+        assert openai_entry["configured"] is True
+
+    @patch("app.api.settings.get_all_settings_from_db")
+    def test_list_credentials_unconfigured_when_no_value(self, mock_db_settings):
+        """Test that credentials with no value are marked as unconfigured."""
+        import asyncio
+
+        from app.api.settings import list_credentials
+
+        mock_db_settings.return_value = {}
+        mock_request = MagicMock()
+        mock_db = MagicMock()
+        mock_admin = {"is_admin": True}
+
+        with patch("app.api.settings.settings") as mock_settings:
+            mock_settings.openai_api_key = None
+
+            result = asyncio.get_event_loop().run_until_complete(
+                list_credentials(mock_request, mock_db, mock_admin)
+            )
+
+        openai_entry = next(c for c in result["credentials"] if c["key"] == "openai_api_key")
+        assert openai_entry["configured"] is False
+        assert openai_entry["source"] is None
+
+    @patch("app.api.settings.get_all_settings_from_db")
+    def test_list_credentials_counts_are_accurate(self, mock_db_settings):
+        """Test that configured_count and unconfigured_count are correct."""
+        import asyncio
+
+        from app.api.settings import list_credentials
+
+        mock_db_settings.return_value = {"openai_api_key": "sk-db-key"}
+        mock_request = MagicMock()
+        mock_db = MagicMock()
+        mock_admin = {"is_admin": True}
+
+        with patch("app.api.settings.settings") as mock_settings:
+            # Most keys will be None, one will be set via db_settings mock
+            mock_settings.openai_api_key = "sk-key"
+
+            result = asyncio.get_event_loop().run_until_complete(
+                list_credentials(mock_request, mock_db, mock_admin)
+            )
+
+        assert result["total"] == len(result["credentials"])
+        assert result["configured_count"] + result["unconfigured_count"] == result["total"]
+
+    @patch("app.api.settings.get_all_settings_from_db")
+    def test_list_credentials_raises_500_on_exception(self, mock_db_settings):
+        """Test that list_credentials raises HTTP 500 on unexpected errors."""
+        import asyncio
+
+        from fastapi import HTTPException
+
+        from app.api.settings import list_credentials
+
+        mock_db_settings.side_effect = Exception("DB failure")
+        mock_request = MagicMock()
+        mock_db = MagicMock()
+        mock_admin = {"is_admin": True}
+
+        with pytest.raises(HTTPException) as exc_info:
+            asyncio.get_event_loop().run_until_complete(
+                list_credentials(mock_request, mock_db, mock_admin)
+            )
+        assert exc_info.value.status_code == 500
+
+    def test_list_credentials_endpoint_requires_admin(self, client):
+        """Test that GET /api/settings/credentials requires admin access."""
+        response = client.get("/api/settings/credentials")
+        assert response.status_code in [302, 401, 403]
+
+    @patch("app.api.settings.get_all_settings_from_db")
+    def test_list_credentials_response_has_required_fields(self, mock_db_settings):
+        """Test that each credential entry has the required fields."""
+        import asyncio
+
+        from app.api.settings import list_credentials
+
+        mock_db_settings.return_value = {}
+        mock_request = MagicMock()
+        mock_db = MagicMock()
+        mock_admin = {"is_admin": True}
+
+        with patch("app.api.settings.settings") as mock_settings:
+            mock_settings.openai_api_key = None
+
+            result = asyncio.get_event_loop().run_until_complete(
+                list_credentials(mock_request, mock_db, mock_admin)
+            )
+
+        for cred in result["credentials"]:
+            assert "key" in cred
+            assert "category" in cred
+            assert "description" in cred
+            assert "configured" in cred
+            assert "source" in cred
+            assert "restart_required" in cred