Anticoagulant therapy includes heparin, either unfractionned or of low molecular weight, danaparoid, vitamin K antagonists and direct thrombin inhibitors. Low molecular weight heparins are now the cornerstone of venous thromboembolism prevention in surgery, and once daily regimen is available for the treatment of acute deep vein thrombosis. Vitamin K antagonists are mostly used for secondary prevention of venous thromboembolism and for primary prevention of arterial embolism in patients with permanent atrial fibrillation or with cardiac prosthetic valve. Thrombotic complications of heparin-induced thrombocytopenia are prevented and treated by direct thrombin inhibitors or danaparoid.