This Medicare Learning Network (MLN) Matters® Special Edition Article is intended for all providers and suppliers who are enrolled in Medicare and required to revalidate through their Medicare Administrative Contractors (MACs), including Home Health & Hospice MACs (HH&H MACs), Medicare Carriers, Fiscal Intermediaries, and the National Supplier Clearinghouse (NSC)). These contractors are collectively referred to as MACs in this article. This article was revised on June 15, 2017, to change the effective date of deactivations due to non-billings from 5 days from the date of the deactivation letter to 10 days. (See page 6.) All other information is unchanged.