Group libraries allow multiple Zotero users to contribute to a shared folder that can be viewed or edited by the group's members.
To create a group library, simply go to Zotero.org, sign in, and click on the "Groups" tab. From there, you can click on "Create a New Group," add members (using their Zotero usernames), and set your privacy and editing settings for the group.
Group folders will appear in your Zotero library beneath your own folders and can be managed and edited in the exact same way as your individual folders.
