Following vascular injury, one of the most critical initial events is activation of platelets followed by formation of a hemostatic plug. Platelets are capable of responding to a diverse array of agonists resulting in adhesion and granule release. The biochemical events underlying platelet activation are just beginning to be understood. One class of molecules shown to play important roles in this process is adapters. Adapter molecules contain distinct modular domains which mediate protein-protein or protein-lipid interactions giving these proteins the ability to nucleate signal transduction complexes. In this review we will discuss the function of the hematopoietic cell specific adapter molecule, SLP-76 in both platelet activation and hemostasis. Because many parallels exist between signal transduction pathways in platelets and lymphocytes, we will also review the function of SLP-76 in coordinating signal transduction pathways following antigen bind to the T cell receptor.