If you already have an extensive library stored in another citation management tool, such as RefWorks, EndNote, etc., you may want to transfer it to Zotero.
To import your libraries into Zotero, start by exporting the bibliographic data from your other software program.
Next, in Zotero, click File and select “Import…”. Browse to your file, select it, and click the “Open” button. This should import the exported items into your Zotero library in a date-stamped collection.
For detailed instructions on how to make the switch from Endnote to Zotero, see Importing Records From EndNote.
Zotero can import amongst others the following bibliographic file formats:
Note: import/export is generally not recommended for transferring entire Zotero libraries between different Zotero installations. Import/export usually does not give you an exact copy of your Zotero library, and, if you use Zotero's word processor plugins, any links to Zotero items from existing word processor documents will be lost after recreating a Zotero library via export/import. Instead, you can use Zotero's sync features or manually copy the Zotero data directory.