This chapter focuses on the reasons why social status has such a profound effect on health and well-being. Even though the root causes of social disadvantage are many, it also focuses on the health-related effects of disadvantage. In an attempt to better understand the psychosocial determinants of the health gradient, the chapter reviews the biological and social determinants of health. One of the key insights of the chapter is that the way social status affects health may be quite different depending on whether people find themselves in a stable versus more unstable situation. Important as social status is, a key insight from social identity theory is that low social status or disadvantage will not always be associated with lower self-esteem. It is important to distinguish between positive and negative sources of social support and to recognise that whereas some forms of social identification will have positive implications for health and well-being, others will not.