A post office is a customer service facility forming part of a national postal system. Post offices offer mail-related services such as acceptance of letters and parcels; provision of post office boxes; and sale of postage stamps, packaging, and stationery. In addition, many post offices offer additional services: providing and accepting government forms (such as passport applications), processing government services and fees (such as road tax), and banking services (such as savings accounts and money orders). The chief administrator of a post office is a postmaster.

Prior to the advent of postal and ZIP codes, postal systems would route items to a specific post office for receipt or delivery. In 19th-century America, this often led to smaller communities being renamed after their post offices, particularly after the Post Office Department ceased to permit duplicate station names within a state.