Zotero can directly import from an online Mendeley library. Due to changes by Mendeley, it's not possible to import from a local Mendeley installation on your computer.

To import your Mendeley library, follow these steps:

1. Make sure that all data and files have been synced to Mendeley servers.
   • If you use Mendeley Desktop, check your sync settings to make sure that data and files are being synced, and confirm that you can open PDFs in your online Mendeley library.
   • If you use Mendeley Reference Manager, your data and files are already all online.
2. Install Zotero 6, which contains the latest version of the importer as well as a new PDF reader that can display PDF annotations imported from Mendeley.
3. Go to File → Import within Zotero and choose the “Mendeley Reference Manager (online import)” option.

You'll be asked to log in to Mendeley to allow Zotero to perform the import. Your Mendeley password is never seen or stored.

If for some reason you're not able to perform a direct online import, it's possible to import from a local Mendeley database by installing an old version of Mendeley Desktop from before Mendeley began encrypting the local database. See the local import instructions for more information.

There are a few issues to be aware of when importing from Mendeley.

• To import PDF highlight and note annotations, you must import using Zotero 6, which adds support for annotations. If you’ve previously imported from Mendeley using Zotero’s importer, you can repeat the process with Zotero 6 to bring in your highlights and notes.
• It’s not possible to directly import group libraries. To import items in group libraries, simply copy the group items to a collection in your Mendeley library before importing. You can then create a Zotero group and drag imported collections or items to that group.
• Mendeley allows any field to be added to any type. When importing into Zotero, if a field isn’t valid for a given item type, the field is placed into the Extra field. When possible, those will be used automatically in citations (e.g., Original Date), and future versions of Zotero will automatically convert those to any real fields that become available.
• When using the Zotero word processor plugins, document citations created with Mendeley won’t currently be linked to imported citations in your Zotero database. Zotero’s word processor plugins can, however, read Mendeley Desktop citations and their embedded metadata, so you can continue using the same documents with Zotero and insert additional instances of those citations by choosing from the “Cited” section of the search results in the citation dialog. Citations created with Mendeley Cite are not readable in Zotero.

Make sure you’re running the latest version of Zotero available via Help → “Check for Updates…”.

If you’re running the latest version and something doesn’t come through how you expect or you run into any trouble, let us know in the Zotero Forums.

Starting in Mendeley Desktop 1.19, Elsevier began encrypting the local Mendeley database, making it unreadable by Zotero and other standard database tools. Elsevier made this change a few months after Zotero publicly announced work on an importer, despite having long touted the openness of its database format as a guarantee against lock-in and explaining in its documentation that the database could be accessed using standard tools. Until recently, Mendeley Desktop imported data from Zotero’s own open database, as it had since 2009.

The Mendeley 1.19 release notes claimed that the encryption was for “improved security” on shared machines, yet applications rarely encrypt their local data files, as file protections are generally handled by the operating system with account permissions and full-disk encryption, and anyone using the same operating system account or an admin account can already install a keylogger to capture passwords. Elsevier later stated that the change was required by new European privacy regulations — a bizarre claim, given that those regulations are designed to give people control over their data and guarantee data portability, not the opposite — and continued to assert, falsely, that full local export was still possible, while repeatedly dismissing reports of the change as “#fakenews”.

Direct access to the Mendeley database is the only local way to export the full contents of one’s own research. The export formats supported by Mendeley don’t contain folders, various metadata fields (date added, favorite, and others), or PDF annotations. Mendeley offers a web-based API, but it contains only uploaded data, so relying on it means that anyone wanting to export their own data first needs to upload all their data and files to Elsevier’s servers. The API is under Elsevier’s control and can be changed or discontinued at any time.

Since making this change, Elsevier has released its replacement for Mendeley Desktop, Mendeley Reference Manager, which is essentially a wrapper around the website and doesn’t contain a real local database at all.