Highlight the addressbook, Right-click and select Export and there is a choice, one of which is csv.

Had exactly this problem. David's solution is fine provided it is clearly spelt out that you MUST SELECT a SPECIFIC Address Book. The default choice of the software is 'All Address Books' which, for some reason, cannot be exported as a .csv file, but only as a very large .zip file containing all accounts, messages, address books, and settings information.

In my case, selecting 'Personal Address Book', (located directly below the 'All Address Books' button/bar), then highlighting ALL of its contents, followed by placing the cursor over the 'Personal Address Book' button/bar, (top LHS of the screen) and right clicking the button/bar brought up the correct dialogue box. Click 'export', and a new dialogue box named 'Export Address Book' is created, containing a file named 'Personal Address Book' in .csv format which can be saved to a destination of your choice. Click 'Save' to complete the process.