This is a detailed geological study of a very important area to British Pleistocene geology. The Middle Thames Valley extends from Goring near Reading to Central London, and includes the largest single spread of river terrace deposits in the country. These deposits record the Thames' history over the last million years, and have been studied in detail by the author. The deposits largely comprise spreads of gravel and sand. The sedimentary environment they represent is discussed. Associated with these spreads are fossiliferous deposits including those bearing fossil pollen, plant remains, vertebrates and other groups. Several previously undiscovered sequences have been studied and the results are summarised. The vertebrate assemblages from the gravel spreads are also assessed. The deposits include the greatest concentration of Paleolithic flint handaxes in Britain. These assemblages are related to the sedimentary environments and the events reconstructed from the geological evidence. The stratigraphical sequence reconstructed by combining all the available evidence provides the first detailed geological history of the River Thames, which in turn reflects the evolution of lowland south-eastern Britain.