Zotero will search for duplicate records within your Library folder. If you have moved the same record to multiple collections, Zotero will not list this as a duplicate resource. If the same article was added twice to your library, Zotero will list this as a duplicate item.

For more information on how Duplicate Detection works in Zotero, click  here.

To find the duplicates in your collection and remove / "merge" the records:

1. Open Zotero.

2. Click "Duplicate Items".

3. You should now see a list of articles Zotero is identifying as duplicates. If no duplicates were found, there would be no articles listed in the window pane.

4. When you click on one of the duplicate resources, the other resource(s) Zotero is identifying as a duplicate will also be selected. If the resources are actually duplicates, select "Merge 2 items" from the far right window. 

5. You will need to do this for each duplicate article.