Liberty is contested because it is complex. It is not merely a concern of political science or economy, an abstract philosophical concept, or a theological doctrine. It is all those things and many things besides; it is, as Lord Acton said, “the delicate fruit of a mature civilization.” To understand this complex and contested idea, the best place to begin is with Acton himself, the foremost historian of liberty. This collection of Acton’s most important historical and moral essays introduces contemporary readers to his account of the emergence and impact of the idea of liberty.