How do I limit access to a specific group rather than allowing access to my entire library? I suspect that there is a setting for this, but I can't find it...
If you actually mean _group_, that's from the the group settings which you can access from https://www.zotero.org/groups If you mean collection within your library, that's not possible.
Just to make sure I understand, if I go to https://www.zotero.org/groups, then to a specific group in the list, and click on "group library", I will be taken to that group within my library. Will the people that I make members of that group, be limited to accessing only collections within that group or will they have access to my entire library?
People with access to a specific group will have access to that group and nothing else related to your account. The only way anyone can view your personal library ("My Library") is if you specifically set it to public here: https://www.zotero.org/settings/privacy. I think you are thinking of this in a way that worries you more than necessary: the groups aren't "within your library." Each group is an independent library with independent permissions. Zotero shows you all libraries to which _you_ have access.
You can set exactly what who can do what for each group under "Manage Library" and you can invite and remove folks under "Manage Members".
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If you mean collection within your library, that's not possible.
The only way anyone can view your personal library ("My Library") is if you specifically set it to public here: https://www.zotero.org/settings/privacy. I think you are thinking of this in a way that worries you more than necessary: the groups aren't "within your library." Each group is an independent library with independent permissions. Zotero shows you all libraries to which _you_ have access.
You can set exactly what who can do what for each group under "Manage Library" and you can invite and remove folks under "Manage Members".