This chapter focuses on the role of depression in the development of coronary atherosclerosis and in the aetiology of coronary heart disease (CHD). It evaluates the strength and consistency of the association between depression and future CHD and describes the biological processes that are probably involved. The chapter reviews the existing evidence from longitudinal observational studies that depression and depressive symptoms are associated prospectively with CHD in initially healthy adults. Three studies have used computed tomography (CT) to assess coronary artery calcification, a more direct measure than carotid thickness of the intima-medial layer (IMT) of coronary disease. The chapter outlines the different pathways that may translate depressive emotional experience into CHD. A number of behavioural factors contribute to CHD, including cigarette smoking, certain patterns of alcohol consumption, eating behaviour and physical activity. It is known that psychological stress provokes acute haemostatic responses in healthy individuals and in patients with CHD.