Sometimes it can be big and round; this is known as a Full Moon. Other times, it can look like the letter C, just like one you might draw in a spooky Halloween picture. We call this a Crescent Moon.

Does the provider need to issue a MOON letter with Medicare Advantage (Part C)? Yes. Providers must issue a MOON letter to any Medicare-insured patient, even if a Part C plan insures the patient.