The great Victorian historian Lord Acton urged his colleagues to study ‘problems in preference to periods’. But sometimes periods are problems. ‘Modern’, ‘medieval’ and, for that matter, ‘Victorian’ are not neutral terms that automatically designate particular dates. Each of them implies an interpretation and a sense that an era can be distinguished from what went before and what came after. How, then, should historians periodise the very recent past? The year 1945 once seemed to mark a clear chronological frontier, but we cannot go on living in the ‘postwar’ era forever.