As the world's population continues to grow at a rapid rate, Malthus's classic warning against overpopulation gains ever more importance. An Essay on the Principle of Population (1798) examines the tendency of human numbers to outstrip their resources: better economic conditions lead inevitably to lower mortality rates; poor relief encourages the poorest and most irresponsible to multiply; reproduction exceeds food production. Malthus' argument was highly controversial in its day. Literary England despised him for dashing its hopes for social progress. Today his name remains a byword for active concern about man's demographic and ecological prospects. In this new edition of the essay, Geoffrey Gilbert considers why it was so effective, and ties it to issues of social policy, theology, evolution and the environment.