Microparticles (MPs) are submicron vesicles released from stimulated or apoptotic cells after plasma membrane remodeling. In body fluids, they constitute relevant hallmarks of cell damage. Having long been considered inert debris reflecting cellular activation or damage, MPs are now considered as cellular effectors involved in cell-cell crosstalk. This review focuses on the pathophysiologic significance of MPs in the particular setting of solid graft and cellular transplantation.