This accessible introductory text discusses how people in a pluralistic society such as ours can accept a common social ethic - a publicly justified morality. It presents analyses of the basic concepts, including justifications of liberty, harm to others, private property rights, distributive justice, environmental harms, help to others and offensive behaviour. Gaus acquaints the reader with the major figures in social philosophy - John Stuart Mill, Jeremy Bentham, Thomas Hobbes, John Locke, David Hume, John Rawls, David Gauthier, and Joel Feinberg - as well as recent communitarian philosophers. The basic technical aspects of social philosophy are also introduced: game theory, social choice theory, the ideas rational action, rational bargaining, and public goods. Throughout, helpful short examples and stories are used to illustrate the material.