The session will be composed of three presentations given by experts in their fields. The focus will be on two aspects of platelet roles in physiology and pathology beyond primary hemostasis and will examine platelet inflammatory products in transfusion and in rheumatoid arthritis. The primary physiological roles of platelets are to patrol alongside the vascular arborescence, to detect insulted endothelial cells and to repair damaged endothelial vascular tissue. In doing so, platelets initiate primary hemostasis. Platelets also make cell encounters and engage dialogs with normal circulating cells as well as with foreign cells or microbes. Platelets thus participate in the early phase of immunity, i.e., the innate branch of the immune system, and-in particular-they play a potent inflammatory role. Recent evidence has shown that platelets also infiltrate tissues, especially in association with other blood cells such as leukocytes. This had been observed for decades in pathology but not further explored. The "novel" characteristics of platelets now allow the revisiting of platelet functions and roles in peripheral tissues.