If you have Medicare and other health coverage, each type of coverage is called a "payer." When there's more than one payer, "coordination of benefits" rules decide who pays first. The "primary payer" pays what it owes on your bills first, and then your provider sends the rest to the "secondary payer" to pay. In some cases, there may also be a "third payer." Whether Medicare pays first depends on a number of things. Be sure to tell your doctor and other health care providers if you have coverage in addition to Medicare. This will help them send your bills to the correct payer to avoid delays. Some people with Medicare have other coverage that must pay before Medicare pays its share of your bill. This guide tells how Medicare works with other kinds of coverage and who should pay your bills first. Also available in Spanish.