I have two view controllers that allow changes to the Address Book. The first one lets you add or create an entry based on an ABRedordRef or edit an existing ABRecordRef, by presentation of either ABUnknownPersonViewController or ABPersonViewController. The second one is a standard ABPeoplePickerNavigationController that allows you to view/edit any of the contents of the Address Book. Both views are accessible easily accessible to the use via the main application UITabBarController. How can I determine that changes were made by either view controller, so that I can force data dependency changes to a third separate view controller. I thought that I saw a notification center message that I could subscribe to, but I can't seem to find it again... I don't care if the notification center is the method that should be used, or a delegate protocol or... whatever, I don't care, I just need to know how to detect the change or the need to re-sync with the Address Book. Can someone Please point me in the right direction. Thank you.