This article provides a review of the various types of antiphospholipid (aPL) antibodies and antiphospholipid syndromes, their prevalence, presumed origin, relationship to autoimmunity in general, and their role in the body's defenses and apoptosis. New hypotheses such as the role of antibodies to beta2 glycoprotein I (beta2GPI) and the signaling of toll-like receptors are also discussed, as is the spectrum of clinical manifestations associated with the demonstration of these antibodies, now assumed to be "pathogenic." A distinction is made between antibodies present in sera of patients with a variety of microangiopathic syndromes (MAPS; e.g., HELLP syndrome, thrombotic thrombocytopenic purpura, and thrombotic microangiopathic syndromes). In these conditions, the antibodies might not be "pathogenic" but, alternatively, generated by small vessel endothelial damage. These conditions are differentially referred to as microangiopathic antiphospholipid-associated syndromes, and they should be differentiated from the microvascular occlusions that are seen in the antiphospholipid syndrome. Current treatments of the antiphospholipid syndrome are briefly reviewed.