Anticoagulation therapy is a medical treatment used to prevent blood clots from forming or growing larger in the blood vessels, which is crucial for patients at risk of thromboembolic events such as deep vein thrombosis, pulmonary embolism, or stroke. It involves the use of anticoagulant medications like warfarin, heparin, and newer agents such as direct oral anticoagulants (DOACs), with careful monitoring to balance the risk of bleeding against the benefits of preventing clots.