Within twenty years of victory in the Second World War Britain had ceased to be a world power and her global empire has dissolved into fragments. With what now seems astonishing rapidity, and empire three centuries old, which had reached its greatest extent as late as 1921, was transformed into more than fifty sovereign states. Why did this great transformation come about? Had Britain simply become too weak in a world of superpowers? Had the pressure of colonial nationalism suddenly become overwhelming? Or had the British themselves decided that they no longer needed an empire, and that interests were better served by joining the rich man's club of Europe? In this short book, these and other theories are examined critically. The aim is not to present a detailed narrative of Britain's imperial retreat but to introduce the reader to the current state of debate in a rapidly expanding subject.