The views on the role of platelets in physiology and in pathogenesis have considerably changed in the recent past. While platelets had previously been seen only as contributors in primary haemostasis and as donors of negatively charged phospholipids to support thrombin formation, this view has had to be revised, at least since the discovery of specific receptors for coagulation factors on the platelet surface. Platelets are part of the body's immune defence system. They can interact with bacteria, pathogenic fungi and protozoa. The interaction of platelets with endothelial cells and leukocytes is crucial in innate and adaptive immunity. Platelets participate in the pathogenesis of the initial lesions and in the progression of atherosclerosis by inducing chronic inflammatory processes at the vascular wall, which result in the development of atherosclerotic lesions and atherothrombosis.