A Medigap policy is a private health insurance policy that covers some of the gaps in Medicare coverage, such as deductibles and coinsurances. Medigap plans have no provider network restrictions and can be used to cover services at any doctor or facility in the U.S. that participates with Medicare billing. Some Medigap plans provide benefits that Medicare doesn’t offer, like coverage out of the country. You must be enrolled in Medicare A and B to be eligible to enroll in a Medigap plan. Medigap plans can be used with original Medicare and Part D plans but cannot be combined with a Medicare Part C plan.