This book explores how different ideas of the common good may be compared, contrasted and ranked.This book presents an exploration of the idea of the common or social good, extended so that alternatives with different populations can be ranked. Principles that rank alternatives are called population principles. They make it possible to rank alternative histories of the world, such as those that arise in environmental discussions, according to their goodness. In addition to examinations of the various principles, optimal poocoes are also discussed and applications to population policies are investigated.This book presents an exploration of the idea of the common or social good, extended so that alternatives with different populations can be ranked. Principles that rank alternatives are called population principles. They make it possible to rank alternative histories of the world, such as those that arise in environmental discussions, according to their goodness. In addition to examinations of the various principles, optimal poocoes are also discussed and applications to population policies are investigated.This book presents an exploration of the idea of the common or social good, extended so that alternatives with different populations can be ranked. Basing rankings on the well-being, broadly conceived, of those who are alive (or ever lived), the axiomatic method is employed. Topics investigated include the measurement of individual well-being, social attitudes toward inequality of well-being, the main classes of population principles, principles that provide incomplete rankings or rank uncertain alternatives, best choices from feasible sets, and applications.1. Introduction; 2. The measurement of individual well-being; 3. Welfarist social evaluation; 4. Fixed-population principles; 5. Population principles; 6. Characterizations and possibilities; 7. Uncertainty and incommensurabilities; 8. Independence and the existence of the dead; 9. Temporal consistency; 1l³4