We are often faced with choices that involve the weighing of people's lives against each other, or the weighing of lives against other good things. These are choices both for individuals and for societies. We have to choose between the convenience to ourselves of road and air travel, and the lives of the future people who will be killed by the global warming we cause. We make choices that affect how many lives there will be in the future: as individuals we choose how many children to have, and societies choose tax policies that influence people's choices about having children. How should we weigh lives? John Broome develops a theoretical basis for answering this practical question. Using some of the precise methods of economic theory (accessible without mathematical expertise), Broome's conclusions will be highly significant for political theorists and economists as well as for philosophers, and anyone concerned with the value of life.