"Classical Utilitarianism," which is best known for arguing that "it is the greatest happiness of the greatest number that is the measure of right and wrong," was developed by the radical philosophers, critics, and social reformers William Godwin, Jeremy Bentham, John Stuart and Harriet Taylor Mill, and Henry Sidgwick. Together, they had a profound influence on nineteenth-century reforms, in areas ranging from law, politics, and economics to morals, education, and women's rights, and key elements of their views are today being revived by some of the world's leading philosophers and economists, notably Peter Singer. This talk, based on my recent book, will highlight a number of the reasons why the views of the classical utilitarians are being revisited and redeployed to address some of the world's most pressing ethical problems.