[Video](https://www.youtube.com/watch?v=ZGraiS9m80U)

Google Drive maintains an automatic history of modifications, which can help
users track file changes and content revisions. In the revision history, users
can see what edits have been made and can revert to a specific version of a file
with specific edits.

The following terms are relevant to the changes and revisions resources of the
Google Drive API:

*Access Control List (ACL)*
:   The list of all permission resources associated with a file, folder, or shared
    drive.

*Change*
:   An alteration made to a file's content or metadata of a file or shared drive.

*User change log*

:   A record of all changes that a user made to every editable file in their My
    Drive, such as a Google Docs, Sheets, or a
    Slides. For members of a shared drive, the user change log
    also includes entries about shared drive membership, user access levels to
    items in that shared drive, and shared drive name changes.

    > [!NOTE]
    > **Note:** Even if several users can access the same file, not all changes to that file are reflected in every users' change log. For example, when a user opens the file for the first time, or marks the file as Starred, those changes only appear in that users' change log. As another example, when a file's ACL is changed, it's only reflected in the change log of the following users: The file's owner, any service accounts on the ACL, and any users directly impacted by the ACL change.

*Shared drive change log*

:   A record of all changes to a shared drive, such as additions or removals of
    users, and all changes to items on that shared drive. A change to an item
    within a shared drive appears in both the *user change log* and shared drive
    change log.

*Change log entry*

:   A record of a change made to a file's content or metadata of a file or shared
    drive. A change log entry indicates the user who made the change, the
    timestamp, and an ID. There can only be one entry per file or shared drive
    in the change log at a time. Each time that file or shared drive changes, a
    new ID is created for that entry, and it replaces the previous entry.

*Revision*

:   A version of the file representing a change to the file's contents (not
    metadata). Each revision can be accessed using the [`revisions`](https://developers.google.com/workspace/drive/api/reference/rest/v3/revisions) resource within the Drive API.

*Head revision*

:   The most current version of a file. The `headRevisionId` can be accessed using
    the [`files`](https://developers.google.com/workspace/drive/api/reference/rest/v3/files) resource within the
    Drive API. The `headRevisionId` is only available for blob files
    in Drive.

*Blob revision*

:   A version of an unmodifiable binary file, such as an image, video, or PDF. If
    the blob revision is the only revision of the binary file, it cannot be
    deleted. A new blob can be uploaded as a new *revision* , which becomes the
    new *head revision* of that file.

    Any blob file revision, other than the head revision, that's not designated
    as "Keep Forever" is purgeable. Purgeable revisions are typically preserved
    for 30 days, but can be purged earlier if a file has 100 revisions that
    aren't designated as "Keep Forever" and a new revision is uploaded.

    For more information on setting blob revisions as "Keep Forever", see
    [Specify revisions to save from auto
    delete](https://developers.google.com/workspace/drive/api/guides/manage-revisions#specify-revisions).

*Revision history*

:   A record of all revisions of a file in chronological order. A change to a
    Docs, Sheets, or Slides file
    gets a new revision. Each time the content changes, Drive
    creates a new revision history entry for that file. However, these editor
    file revisions may be merged together, so the API response might not show
    all changes to a file.

## Related topics

- To identify where the change you want to track is recorded, see [Identify
  which change log to track](https://developers.google.com/workspace/drive/api/guides/about-changelogs).
- To set up change tracking for users and shared drives, see [Track changes
  for users and shared drives](https://developers.google.com/workspace/drive/api/guides/about-changes).
- To download a blob file content revision or to export a Google Workspace document content revision, see [Download and export
  files](https://developers.google.com/workspace/drive/api/guides/manage-downloads).
- To publish a revision, see [Manage file
  revisions](https://developers.google.com/workspace/drive/api/guides/manage-revisions).
- To set up change notifications, see [Notifications for resource changes](https://developers.google.com/workspace/drive/api/guides/push).