This proposed session will explore recent developments in our understanding of the effect of transfusion interventions and diagnostic tests in major bleeding. A common massive hemorrhage protocol cannot be recommended for all causes of major bleeding, and interventions need to be tailored by cause of bleeding. For example, patients with major bleeding due to gastrointestinal need a different management approach to those with obstetric bleeding or trauma (red cell transfusions, tranexamic acid). Many centers that treat massively bleeding patients rely on viscoelastic hemostatic assays to provide information about the coagulation status of their patients. Recently a large randomized trial of injured patients found that bleeding and survival was not different between patients resuscitated with either a viscoelastic or conventional coagulation strategy. This talk will review this and other studies on diagnostic tests and discuss our current standards for monitoring major bleeding.