The Thames is a major river flowing through southern England. While best known because its lower reaches flow through central London, the river flows through several other towns and cities, including Oxford, Reading and Windsor.

The river gives its name to the Thames Valley, a region of England centred around the river between Oxford and West London, the Thames Gateway, the area centred around the tidal Thames, and the Thames Estuary to the east of London.

The River Thames is the longest river entirely in England, rising officially at Thames Head in Gloucestershire, and flowing into the North Sea at the Thames Estuary. It has a special significance in flowing through London, the capital of the United Kingdom, although London only touches a short part of its course. The river is tidal in London with a rise and fall of and becomes non-tidal at Teddington Lock. The river contains over 80 islands, and having both seawater and freshwater stretches supports a variety of wildlife.