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+++ b/docs/user_guide.md
@@ -5,6 +5,7 @@ This guide walks you through the fundamentals of using Harbor. You'll learn how
 * [Manage your projects.](#managing-projects)
 * [Manage members of a project.](#managing-members-of-a-project)
 * [Replicate projects to a remote registry.](#replicating-images)
+* [Retag images within Harbor](#retag-images)
 * [Search projects and repositories.](#searching-projects-and-repositories)
 * [Manage labels.](#managing-labels)
 * [Manage Harbor system if you are the system administrator:](#administrator-options)
@@ -165,8 +166,23 @@ The system administrator can also operate the replication rules defined for the
 
 ![browse project](img/rule_under_project_view.png)
 
+## Retag Images
 
-## Searching projects and repositories  
+Images retag helps users to tag images in Harbor, images can be tagged to  different repositories and projects, as long as the users have sufficient permissions. For example,
+
+```
+release/app:stg  -->  release/app:prd
+develop/app:v1.0 --> release/app:v1.0
+```
+To retag an image, users should have read permission (guest role or above) to the source project and write permission (developer role or above) to the target project.
+
+In Harbor portal, select the image you'd like to retag, and click the enabled `Retag` button to open the retag dialog.
+
+![retag image](img/retag_image.png)
+
+In the retag dialog, project name, repository name and the new tag should be specified. On click the `CONFIRM` button, the new tag would be created instantly. You can check the new tag in the corresponding project. 
+
+## Searching projects and repositories
 Entering a keyword in the search field at the top lists all matching projects and repositories. The search result includes both public and private repositories you have access to.  
 
 ![browse project](img/new_search.png)