When are you required to transmit your assigned call sign?

The fundamental rule for station identification in amateur radio is that you must transmit your assigned call sign at least every 10 minutes during an ongoing communication, as well as at the end of that communication. This allows the FCC and other operators to easily identify who is using the frequency. You are actually not legally required to transmit your call sign at the very beginning of a contact, although it is a standard and polite operating practice to do so. Distractors suggesting identification every 15 minutes or during every single transmission are incorrect and would cause unnecessary clutter on the air.