How can I move my Zotero library to a different computer?
Option A: Copy the data directory
The most reliable way to move your entire library to another computer is to copy the Zotero data folder from your first computer to your new computer.
Be sure to close Zotero on both machines before copying the Zotero files. If you've already opened Zotero on the new computer, there will already be a Zotero data directory with an empty database, and you should delete the whole data directory before copying the new directory to the same location.
Option B: Enable Zotero Sync
You can also automatically sync your library between multiple computers via the Zotero servers.
Exporting and importing your library (for instance via Zotero RDF) is not a recommended option. None of the available export formats allow for a complete transfer of your library data, reimporting will break connections with any existing word processor documents, and if you use syncing later you will end up with duplicates of any imported items.