For most of history, antisemitism has been understood as a menace from Europe’s political Right, the province of blood-and-soil ethno-nativists who built on Christendom’s long-standing suspicion of its Jewish population and infused it with racist pseudo-science. Such threats culminated in the nightmare of Nazi Germany and the Holocaust. The landscape is very different now, as Mark Mazower argues in this piercingly brilliant book. More than four-fifths of the world’s Jews now live in Israel and the United States, with the former’s military dominance of its region guaranteed by the latter while the loudest voices decrying antisemitism see it coming from the Left not the Right. Mazower clearly and carefully shows us how we got here, seeking to illuminate rather than blame. Very few words have the punch of ‘antisemitism’ and yet no term is more liable to be misunderstood in ways affecting free speech and foreign policy alike. On Antisemitism is a vitally important attempt to draw a line that must be drawn.