The antiphospholipid syndrome causes venous, arterial, and small-vessel thrombosis; pregnancy loss; and preterm delivery for patients with severe pre-eclampsia or placental insufficiency. Other clinical manifestations are cardiac valvular disease, renal thrombotic microangiopathy, thrombocytopenia, haemolytic anaemia, and cognitive impairment. Antiphospholipid antibodies promote activation of endothelial cells, monocytes, and platelets; and overproduction of tissue factor and thromboxane A2. Complement activation might have a central pathogenetic role. Of the different antiphospholipid antibodies, lupus anticoagulant is the strongest predictor of features related to antiphospholipid syndrome. Therapy of thrombosis is based on long-term oral anticoagulation and patients with arterial events should be treated aggressively. Primary thromboprophylaxis is recommended in patients with systemic lupus erythematosus and probably in purely obstetric antiphospholipid syndrome. Obstetric care is based on combined medical-obstetric high-risk management and treatment with aspirin and heparin. Hydroxychloroquine is a potential additional treatment for this syndrome. Possible future therapies for non-pregnant patients with antiphospholipid syndrome are statins, rituximab, and new anticoagulant drugs.