The state postal system and telecommunications carrier of the United Kingdom until 1969. Before the Acts of Union 1707, it was the postal system of the Kingdom of England, established by Charles II in 1660. Similar General Post Offices were established across the British Empire.

Originally, the GPO was a state monopoly covering the dispatch of items from a specific sender to a specific receiver, which was to be of great importance when new forms of communication were invented.

The creation of the GPO, then the General Letter Office, was legislated for by the Parliament of England after The Restoration, which returned the British Isles to monarchy under the House of Stuart. The postal service was known as the Royal Mail because it was built on the distribution system for royal and government documents.

An earlier system had been set up under the republican Commonwealth of England, Scotland, and Ireland in 1657 under a Postmaster General, whose office was created anew in 1661 and existed until its abolition, along with the GPO itself, by the Post Office Act 1969