Larry May has written a book on crimes against humanity that provides careful analysis of the core issues for anyone – whether lawyer, moral or political philosopher, or plain citizen – interested in this subject. The book is divided into four parts. In the first two, May explores the philosophical underpinnings of the concept of crimes against humanity, arguing for his own preferred version of it, and he examines some of the most relevant norms of international law. The third and fourth parts are then concerned with matters of (roughly) application: here he discusses, amongst other topics, difficulties in prosecuting individuals putatively responsible for crimes against humanity (including genocide), the idea of the international rule of law, and what there is to be said for amnesty and reconciliation programmes. Although there is much of interest in these later sections of the book, my review will focus on the argument of its first two parts: that is, on the philosophical case the author lays out and the normative principles central to it. His approach to thinking about crimes against humanity is, so I shall contend, at once instructive and flawed.