The present invention identifies P-selectin as a modulator of hemostasis. Accordingly, the present invention relates to methods for the identification and use of modulators of P-selectin activity as modulators of hemostasis. The invention also relates to methods and compositions for the diagnosis and treatment of hemostatic disorders, including, but not limited to, hemorrhagic disorders and thrombotic disorders. The present invention describes methods for the diagnostic evaluation and prognosis of various hemostatic conditions, and for the identification of subjects exhibiting a predisposition to such conditions. In addition, the present invention provides methods for the diagnostic monitoring of patients undergoing clinical evaluation for the treatment of a hemostatic or vascular disorders, and for monitoring the efficacy of compounds in clinical trials.