Open the address book window Make sure the Directory Pane is showing on the left side with all your book folders in it. View-Layout-Directory Pane Click on the folder of the book your want to move contacts FROM so it displays in the main window. Select the contacts to move. select one contact to get focus on the book and then control+a will select all I suggest that you copy the contacts and not move them. This way you can confirm that all contacts are in the new book before deleting the old book. You could also export the book before the move so you have a backup file in case something goes wrong. To copy instead of move you will hold the control key while dragging the selected contacts to the new book folder and drop them there. You will see a + sign beside the moving contacts to indicate a copy. When you are sure everything got moved over you can delete the old book. Repeat as needed for other books. The Personal and the Collected books are the default address books in Thunderbird. I would combine the other books into the Personal book. The Collected book collects addresses that you send mail to.