Antiphospholipid syndrome (APLS) is a complex systemic disease with a wide variety of clinical manifestations. In the obstetric population, recurrent early pregnancy loss, fetal loss, and thrombosis are hallmarks of the disease. Patients with APLS have developed one or more pathogenic auto-antibodies directed against plasma and cell surface proteins. These antibodies are characterized by their affinity for anionic phospholipids. Interactions between APLS antibodies and their protein targets influence a wide variety of biological systems and signaling pathways, including monocytes, platelets, the complement system, and endothelial cells. While much research is currently directed at understanding the mechanisms involved in this autoimmune disease, the key clinical presentation is the hypercoagulable state resulting in thrombosis occurring in essentially any arterial or venous location, as well as numerous obstetrical complications. Treatment of APLS is generally directed at preventing thrombosis and poor pregnancy outcomes by ameliorating the hypercoagulable state.