A brdding colony of the grey seal was studied in the autumn of 1947 at Ramsey Island. The arrival of both sexes at the breeding grounds is discussed and also their behaviour prior to the birth of the calves. The history of the calf while on the beach is summarized, and calving rate, sex ratio and infant mortality are discussed. The movements of the immature and non-breeding population are dealt with, and a description is given of the fur colour and age and sex distinctions. An attempt is made to elucidate population dynamics and the status of the species in South Wales. It is postulated that the Ramsey seals are traditionally cave-breeders and that open beach breeding is a recent habit. Finally a comparison is made between the development and behaviour of Ramsey seals and those of Scottish colonies. It is shown that at Ramsey the adults are less dependent on land and the young are generally more precocious.