Introduction: Policy makers and researchers in health care in most industrial countries have had strained relationships with each other in recent decades. Most researchers in health care and health services have not accorded sufficient attention to what policy makers, and the researchers who study them, know about how policy is made and implemented. Three generalizations, grounded in evidence, are fundamental to understanding policy making in health: 1) New policy to protect or improve health is usually made on the basis of consensus among powerful people about assumptions that underlie and guide policy; 2) Policy makers rarely have a mandate from voters and powerful interest groups to accord the highest priority to achieving lower mortality or improved health status; 3) Professionals in politics and public management have solid reasons to be wary of claims by researchers and their advocates that they ought to change or create particular policies.