Abstract: Poorer people live shorter lives and are more often ill than the rich. This disparity has drawn attention to the remarkable sensitivity of health to the social environment. This publication examines this social gradient in health, and explains how psychological and social influences affect physical health and longevity. It then looks at what is known about the most important social determinants of health today, and the role that public policy can play in shaping a social environment that is more conducive to better health. This second edition relies on the most up-to-date sources in its selection and description of the main social determinants of health in our society today. Key research sources are given for each: stress, early life, social exclusion, working conditions, unemployment, social support, addiction, healthy food and transport policy. Policy and action for health need to address the social determinants of health, attacking the causes of ill health before they can lead to problems. This is a challenging task for both decision-makers and public health actors and advocates. This publication provides the facts and the policy options that will enable them to act.