My experience is that importing from an external file creates a new address book. I'm curious as to how you have achieved a merge. So I'd expect to import and create a new address book, then move its contents to an existing address book, if there was no reason to keep them in their own separate address book. You can move or copy Contacts between address books by drag-and-drop. You need to do this in the actual Address Book window; you can't do it in that Contacts Sidebar in the composition window. Drag-and-drop ''moves'' a Contact. Hold down the ctrl key to change this to a ''copy''.