For those 65 and older, did you know that the Centers for Medicare and Medicaid (CMS) is who actually writes the Medicare Supplement (Medigap) Insurance plans? This means that Medigap insurance companies in most states can only sell you a standardized policy identified by letters A through N. Each standardized Medigap policy must offer the same basic benefits, no matter which insurance company sells it. COST is usually the only difference between plans with the same letter sold by different insurance companies, according to the Centers for Medicare and Medicaid Services Choosing a Medigap Policy Guide.