A post office is a public facility and a retailer that provides mail services, such as accepting letters and parcels, providing post office boxes, and selling postage stamps, packaging, and stationery. Post offices may offer additional services, which vary by country. These include providing and accepting government forms (such as passport applications), and processing government services and fees (such as road tax, postal savings, or bank fees). The chief administrator of a post office is called a postmaster.

Before the advent of postal codes and the post office, postal systems would route items to a specific post office for receipt or delivery. During the 19th century in the United States, this often led to smaller communities being renamed after their post offices, particularly after the Post Office Department began to require that post office names not be duplicated within a state.