Medicare supplement insurance fills the gaps between Medicare benefits and what you must pay out-of-pocket for deductibles, coinsurance, and co-payments. Therefore, it is often called Medigap insurance. Medigap policies only pay for services deemed by Medicare as medically necessary, and payments are generally based on the Medicare-approved charge. Some plans offer benefits that Medicare doesn’t, such as, emergency care while in a foreign country, and preventive health care services. There are 10 standardized Medigap benefit plans, labeled A through J. Each insurance company must use these same identifying letters. All companies that sell Medigap insurance must offer Plan A, but do not have to offer the other nine plans.