While Zotero stores all data locally on your computer by default, Zotero's sync functionality allows you to access your Zotero library on any computer with internet access. Zotero syncing has two parts: data syncing and file syncing.

Data syncing merges library items, notes, links, tags, etc. — everything except attachment files — between your local computer and the Zotero servers, allowing you to work with your data from any computer with Zotero installed and to view your library online on zotero.org. Data syncing is free and unlimited, and it can be used without file syncing.

The first step to syncing your Zotero library is to create a Zotero account (which is also used for the Zotero Forums). Then, open the Sync pane of the Zotero preferences and enter your login information in the Data Syncing section.

By default, Zotero will sync your local data with the Zotero servers whenever changes are made. To disable automatic syncing, uncheck the “Sync automatically” checkbox in this section. You can sync manually at any time by clicking the “Sync with zotero.org” button on the right-hand side of the Zotero toolbar.

When Zotero syncs, it automatically applies changes in both directions — any changes you make in one place will be applied to all other synced computers. If an item has changed in multiple places in conflicting ways between syncs, you'll receive a conflict resolution dialog asking which version you'd like to keep. If you find yourself using a new computer, you can simply set up syncing and Zotero will automatically download all data from your online library.

Data syncing syncs library items, but doesn't sync attached files (PDFs, audio and video files, images, etc.). To sync these files, you can set up file syncing to accompany data syncing, using either Zotero Storage or WebDAV.

Zotero Storage is the recommended file sync option. It has several advantages over WebDAV syncing, including syncing of files in group libraries, web-based access to PDFs and other attachments, easier setup, guaranteed compatibility, and improved upload performance for certain files. Each Zotero user is given 300 MB of free Zotero Storage for attached files, with larger storage plans available for purchase.

See the Zotero Storage documentation for more information.

WebDAV is a standard protocol for transferring files over the web, and it can be used to sync files in your personal library. (Group libraries cannot use WebDAV.) Your employer or research institution may be able to provide WebDAV storage. Otherwise, there are many third-party options, both free and paid (see WebDAV providers known to work with Zotero).

Once you have your WebDAV account info, enter the URL provided by the service, your username, and your password in the Sync preferences tab. Be sure to select 'http' or 'https' as appropriate — if you're not sure, try 'https' first. After entering the information, click “Verify Server”. If Zotero successfully verifies the WebDAV account, you're all set to use file syncing via WebDAV.

Zotero file sync should work with any correctly functioning WebDAV server. Zotero developers cannot provide support for third-party WebDAV servers.

If Zotero is set to sync automatically, changes will be synced within a few seconds of being made. Otherwise, you can start a manual sync by clicking the sync button on the right-hand side of the Zotero toolbar.

If you enter the same login information into the Sync preferences on multiple computers, Zotero will sync everything transparently. Your attention should only be needed if the same item or file is edited in conflicting ways in two different places before Zotero has a chance to sync them. If that happens, you'll be presented with a conflict resolution window, where you can decide which changes to accept.

If you sync from only one computer, you can still view your online library at zotero.org from any computer. Should something happen to your computer or should you want to start using Zotero on another computer, simply set up your account info on the new computer. Zotero will pull down your entire library from the server.

If, for whatever reason, you are unable to use Zotero's syncing features, there are some alternative ways to sync your data, though there are significant risk and limitations depending on the approach that you choose.

Storing the Zotero data directory directly in a cloud storage folder is extremely likely to corrupt your Zotero database and should not be done.

If you want to avoid syncing any data to Zotero servers:

• You can close Zotero, manually copy your entire Zotero data directory to a synced folder on one computer, and then restore it — again with Zotero closed — on another computer, as if you were performing a backup and restore of your data.

If you want to use Zotero data syncing but use an external service to sync just your Zotero attachment files, you have a couple options:

1. The easiest method is to use linked files, rather than stored copies of files, with only your attachment files in the externally synced folder. The ZotFile plugin can make this simple by automatically moving attachment files to a designated folder as you import them. You should also set up Zotero's Linked Attachment Base Directory feature to point to the same folder so that Zotero can find your files on each computer, even if the path to the cloud storage folder differs.
2. Alternatively, you can use a symlink to sync only the storage directory from your Zotero data directory using the external sync service. This will sync your attachment files without touching the main Zotero SQLite database. This is an advanced technique, and if you don't fully understand how to create symlinks and how they interact with your cloud storage service, you should not use it. This method may also interfere with Zotero's full-text indexing processes, so you may need to take manual steps to index newly added files on some devices.