[dwig]

Originally Posted by theducks

Copy the Library folder (safer than mounting as a network drive) to a SEPERATE (from the current Library) folder.

Then start Calibre: right-click the Library Icon:Create-Switch: Use Existing:<choose that folder>. (This 'registers' the Library).

Now Select Books you wish to merge: Right click: Copy TO Library <main library name> ...Wait

Now, right-click the Library Icon: Select old Library

Enjoy

I would add that you should first BACKUP the target library. That way, if the merge fails or produces any undesired results you can simply delete it and revert to the backup copy of the original.