The development of the area of the Thames Estuary is briefly traced since the late Cretaceous period, with its present outline being due to a combination of factors. The overall subsidence of the North Sea area, the `Alpine' fold movements, and the transgression of the sea since the retreat of the Weichselian ice-sheets have all contributed. The positions of the shore-line during the critical phase, 9600 B.P. to 8000 B.P., of this last transgression of the sea are shown. Subsequent to this main transgressive phase, erosion of the shoreline has been rapid due to storm-waves and tidal current action. An estimation of the average rate of subsidence and/or sea-level rise is given based on the concept of sedimentary equilibrium in which a figure of 12.7 cm (5 in) per century is arrived at.