Postal Service, United States, is an independent establishment within the executive branch of the United States government. It provides mail services, including pickup and delivery, and sells postage stamps and postal money orders. The Postal Service is one of the world's largest organizations, with tens of thousands of post offices and hundreds of thousands of employees. The Postal Service began operating in 1971, when it replaced the United States Post Office Department. The Postal Service has headquarters in Washington, D.C.