This article lists the islands in the River Thames, or at the mouth of a tributary (marked †), in England. It excludes human-made islands built as part of the building of forty-five two-gate locks which each accompany a weir, and islets subordinate to and forming part of the overall shape of another. The suffix -ey (pronounced today /iː/) is common across England and Scotland and cognate with ait and meaning island, a term – as ait or eyot – unusually well-preserved on the Thames. A small minority of list entries are referred to as Island, Ait or Eyot and are vestiges, separated by a depression in the land or high-water-level gully.
Most are natural; others were created by excavation of an additional or replacement navigation channel, such as to provide a shorter route, a cut. Many result from accumulation of gravel, silt, wildfowl dung and plant decay and root strengthening, particularly from willows and other large trees. Unlike other large rivers, all today are considered fixed. All in the reaches below Lechlade have been protected against erosion by various combinations of canalisation of the river, building up with dredged material from the river bed, water reeds, concrete, cement, wood or sheet piling.