Platelet-derived microparticles, released as a result of platelet activation, promote coagulation through the surface exposure of phosphatidylserine. Although elevated numbers of circulating platelet-derived microparticles can be detected in a number of clinical disorders, the methods for the detection of these microparticles are far from standardised. In addition, recent reports have also speculated that not all microparticles may expose phosphatidylserine, demonstrating that the binding of annexin V is not detectable on a population of microparticles. This book investigates the procoagulant activity and annexin V binding properties of platelet-derived microparticles.