Hi You might export the address books from two computers, and import them to the main one. To be certain that the imported files will not overwrite anything in the main Thunderbird, rename the address books during export. Or - export all the address books as CSV files, open them in a spreadsheet program, combine all the separate files and delete duplicates, save as csv file and import to the main Thunderbird (and the others if you wish). - Start Thunderbird on a computer whose address books you want to move. - In the Address Book window, select the address book that you want to export. (Note that if you select All address books, each one will be exported separately.) - Go to the "Tools" menu and select "Export...". - Enter a name for (each) address book, - Select "LDIF" from the drop-down list, or CSV if you want to edit them in a spreadsheet, - Choose where on your computer you want to save (each) address book, and then click to save the file. You might put them on a USB drive as you intend moving them to another computer. That makes a backup copy or a copy you can import to Thunderbird. Switch to the main computer - Start Thunderbird. - Go to the "Tools" menu. - Just to be safe, export the address books to LDIF as above, to make a backup in case things go wrong. - Then in Tools, select Import. - Choose to import Address Books -> from Text files. - Next - locate the files you saved from the other computer, or the combined csv file. - Repeat for each of the exported files. I hope that works for you.