An account is given of the various phases of breeding behaviour of both cows and bulls on the island of Shillay, Outer Hebrides. Attention is drawn to unique features of combat between the bulls both before and after taking up territorial positions. The influence of the terrain available upon the behaviour of the seals of all ages is emphasised and comparisons made with other Scottish and Welsh colonies. An attempt is made to draw up a Life-table compatible with the known vital statistics. The more serious gaps in our knowledge of the population dynamics of this species are noted.