Thomas Robert Malthus created a considerable controversy with the 1798 publication of his Essay on the Principle of Population. Since then there has been a great deal of confusion about the ideas attributed to him. Donald Winch here examines the contribution Malthus made to political economy, morality, and demography, and the changes his Essay underwent after its second, mature edition of 1803. He also assesses the profound influence Malthus had on Darwin and Keynes, and his influence on contemporary economic thought.