Summary Summary: Anticoagulant drugs are frequently used in intensive care medicine for prevention and treatment of thromboembolism. Unfractionated heparin, low molecular weight heparins, heparin derivatives, hirudine, and oral anticoagulants have to be used with regard to the clinical situation. In critically ill patients anticoagulant therapy must be individually adapted and meticulously monitored. Profiles of anticoagulant drugs, recommendations for dosage and drug monitoring are presented. Prophylactic treatment of deep vein thrombosis is widely used, however, there is still a lack of controlled studies in this specific clinical setting.