To export your entire library, click on the gear icon in the Zotero toolbar and select Export Library. Group libraries are not included.

You can also select an individual collection or individual items, right-click, and choose the Export option to export only a part of your library.

Please note: Import/export is not recommended for transferring entire Zotero libraries between systems, and, if you use Zotero's word processor plugins, links to Zotero items from existing word processor documents will be lost after an export/import.