Platelets play a role in multiple parts of the hemostatic mechanism, and both genetic and acquired disorders of aggregation, adhesion, activation, secretion and clot retraction have been described. In addition, drugs that impair platelet function are in common use in society, causing symptomatic hemorrhage as well as interference with the planning for surgery and invasive procedures. Platelet transfusion can play a key role in the correction of functional platelet impairment, and transfusion medicine services need to be aware of platelet function disorders. The principles of the testing that aid in the diagnosis and assessment of platelet function abnormalities will be reviewed in this audioconference, including methodologies at the point of care or the bedside as well as in coagulation laboratories. The role that these tests play in guiding platelet transfusion practice will also be reviewed.