Since the mid-1970s, the ancient view that the determinants of health go well beyond medical care has reemerged in most western democracies. Yet despite nearly two decades of repeated intellectual efforts to redirect health policy away from curative medicine to more fundamental interventions, the task remains largely undone. The purpose of this volume is to ask why, and to suggest answers and evidence about the determinants of population health that may help redirect national health policies. The book provides a conceptual framework that permits the integration of evidence arising from a diverse range of disciplines. In particular, it highlights observations that have heretofore been difficult to explain within traditional clinical or health-promotion understandings of what makes some populations healthier than others. Individual chapters explore the role of factors as diverse as culture, genetic predisposition, biological pathways, and social and economic environments. Other chapters discuss how to convert this deepened understanding into changes in health policy. This unusual volume is, in every sense, a collaborative effort, the culmination of several years' interaction among the members of the Population Health Program of the Canadian Institute for Advanced Research (C.I.A.R.). While each chapter has one or more members of this group as designated authors, all chapters reflect the influence of the collaboration, as well as of the distinguished C.I.A.R. colleagues from many disciplines with whom members have interacted since the group's inception in 1987.