The main geological characteristics of five crustal blocks within West Antarctica are summarized in this review. At least some of these blocks existed as Mesozoic microplates and their original, palaeoposition within Gondwana is discussed, together with different break-up models. Links between microplates within the South Atlantic region and a mantle plume beneath southern Africa and Antarctica at the time of breakup (most likely the Bouvet plume) are uncertain, although the plume would appear to have at least controlled the position of breakup, and may even have played a more active role in formation of the microplates and their rotation. Similarily, a mantle plume beneath the Marie Byrd Land margin of West Antarctica may have controlled the position of breakup between New Zealand and Antarctica in Late Cretaceous times. There is much less certainty about the existence of this plume than the initial breakup plume.