A postal service is an organization that collects, transports, and delivers letters and packages from one place to another. When you write a letter to your grandmother across the country, drop it in a mailbox, and she receives it a few days later, the postal service made that happen.

The way it works is remarkably efficient: postal workers collect mail from mailboxes and post offices, sort it by destination at large processing centers, transport it by truck or plane, and deliver it to individual addresses. In the United States, the United States Postal Service (often called USPS or simply the post office) delivers to every address in the country, from apartments in crowded cities to remote cabins in Alaska.

Postal services have existed for thousands of years. Ancient Persian kings created networks of messengers on horseback to carry messages across their empire. In America, Benjamin Franklin served as the first Postmaster General in 1775, helping establish a postal system that connected the colonies. For most of history, the postal service was the only way to send written messages over long distances.

Today, with email and text messaging, people send fewer personal letters than before, but postal services remain essential for delivering packages, bills, official documents, and online shopping orders. When you order something online and it shows up at your door, chances are good the postal service brought it the last part of the way to your home.