Select the source book in the left pane of Address Book, select the contacts in the right pane, drag them onto the target book icon in the left pane while holding Ctrl, drop (release the mouse button).

Thanks SF, On MacOS, I hold down the Control button and select the contact(s), and the popup menu appears with these choices: Write, Print, Delete, Services.

The method above applies to Windows. Is your source book the OS X address book or one native to TB, such as Personal Address Book? Maybe on OS X you press Cmd instead of Ctrl.

Thanks SF, I tried Command but it moves the contact. I also tried Option and that moves the contact too.

Unfortunately, I don't have a mac to try this. Let's see if a mac user sees this, as it's hard to believe there's no way to copy contacts on OS X.

If you can edit the title of this topic, change it to something that attracts attention, e.g. "Copy contacts between address books on mac OS X".

In the absence of a proper method, there is a crude workaround: export (from context menu or ... menu) the source address book to LDIF format, with a different name, then import the LDIF from Tools/Import..., then drag contacts from the imported address book onto the source book icon.