Snake venoms are complex mixtures containing many different biologically active proteins and peptides. A number of these proteins act on components of the hemostatic system in humans. The paper focuses on those venom constituents that affect the blood coagulation pathway, endothelial cells and platelets. Several highly purified venom enzymes have been used clinically as anticoagulants, and other venom proteins are being used in preclinical research to investigate their possible therapeutic potential. Hemostatically active components are distributed widely in the venom of many different snake species. In no case are all the components described below found in any single venom. Venom components can be grouped into several categories depending on their hemostatic effect. The following hemostatically active components are discussed in this chapter: enzymes that cause fibrinogen coagulation: enzymes that degrade fibrin(ogen); plasminogen activator; prothrombin activators; factor V activator; factor X activator; anticoagulant activities: enzymes with hemorrhagic activity; platelet aggregation inducers: and platelet aggregation inhibitors.