Microparticles are submicron-sized vesicles shed from the membranes of a variety of cells in response to cellular activation, mechanical stress or apoptosis. Microparticles form through a process of plasma membrane partitioning that entails a loss of lipid membrane asymmetry, resulting in the exposure of phosphatidylserine normally present on the inner leaflet of the membrane bi-layer. This session will highlight various subpopulations of microparticles, from endothelial to leukocyte to red cell microparticles, and discuss recent insights into the pathways leading to their formation, antigenic characteristics, their interactions with immune cells, their potential relevance to disease and transfusion medicine and the challenges inherent to standardization of microparticle enumeration for translational studies.