How to diagnose Address Book quitting unexpectedly? When opening Address Book, it quits before it opens. The window says:

Address Book quit unexpectedly. Click `Reopen` to open the application again. 
Click `Report` to see more detailed information and send a report to Apple.


What's the best solution? How can I diagnose this problem?
You can click on the Report button and look though all the gibberish to see if there is something informative or suspicious there.

You could run the Console program and search for "Address" in the upper right to check for error messages.

You could try accessing your contacts from within the Mail program and check near the top and bottom of the list for any missing or weird entries.

You could turn on iCloud syncing (if you already have it on, back up) and see if you can access your full contact list from the web interface.

You could check for System Updates and hope there is a new update (Mavericks soon!) of the Contacts app.

** If you ever do get it to open, you should back up your contacts immediately (Export...> Contacts Archive) just in case.