Long term anticoagulation with Vitamin K antagonists (e.g. warfarin) has been shown to reduce major thromboembolic complications in patients with many common chronic conditions, including atrial fibrillation, history of deep vein thrombosis and pulmonary embolism, and mechanical heart valves. However, Vitamin K antagonists have a very narrow therapeutic window requiring frequent laboratory monitoring to ensure that patients are neither excessively anti-coagulated, which increases the risk for bleeding, or under anti-coagulated, which increases the risk for thromboembolism. Laboratory monitoring consists of measuring the blood's tendency to clot with a test known as the International Normalized Ratio (INR), usually performed every 4-6 weeks. Dosage adjustments are then based on these results. Since management of long term oral anticoagulation requires frequent testing and dose adjustment, anticoagulation clinics (ACC) have been developed to streamline and standardize this care. Typically run by specially trained nurses or pharmacists, these clinics provide intense patient education, provide timely follow-up of INR results, use algorithms for dose adjustments, and are easily accessible to patients between visits. More recently, portable devices have become available that are able to accurately measure the INR with a drop of capillary blood. This means that patients can now test themselves at home and either call in the result to their provider who suggests dosage adjustments (known as patient self testing, PST) or adjust their dose of medication themselves (known as patient self management, PSM). As a leader in safety and quality, the Department of Veterans Affairs (VA) is interested in assuring that veterans on long-term anticoagulation receive state-of-the-art care that maximizes efficacy and minimizes complications. Towards that end, this review was commissioned by the VA's Evidence-based Synthesis Program, in conjunction with the Office of Quality and Performance. The final key questions are: 1. For management of long-term outpatient anticoagulation in adults, are specialized anticoagulation clinics (ACC) more effective and safer than care in non-specialized clinics (e.g., primary care clinics, physician offices)? 1a. Which components of a specialized anticoagulation clinic are associated with effectiveness/safety? 2. Is Patient Self Testing (PST), either alone or in combination with Patient Self Management (PSM), more effective and safer than standard care delivered in either ACCs or non-specialized clinics? 3. What are the risk factors for serious bleeding in patients on chronic anticoagulant therapy?