Flow cytometry is a powerful and versatile tool which can be used to rapidly measure the specific characteristics of a large number of individual platelets, providing substantial information on their phenotype and function. This encompasses multiple assays for multiple purposes, including measurement of surface expression of functional receptors, bound ligands, expression of granule components, calcium flux, intracellular signalling, platelet-platelet aggregation, platelet-leukocytes interactions, formation of microvesicles and interaction of platelets with the coagulation system. Measurements may be of circulating platelets in whole blood, or the response of platelets to chemical agonists directed at specific pathways. Assessment of these characteristics may facilitate the diagnosis of inherited or acquired disorders of platelet number and function, predict risk of cardiovascular events, or assist in the monitoring and guidance of antiplatelet therapy.