Systemic lupus erythematosus (SLE) is the prototypical autoimmune disease, associated with autoantibody production and evidence for immune complex deposition among the many aspects of its pathophysiology. SLE occurs most commonly in women during their reproductive years. The disease is approximately nine times more common among women than men. Virtually any organ can be affected by SLE. However, constitutional symptoms, mucocutaneous features, mus-culoskeletal involvement, and renal and central nervous system disease are the most common manifestations. Many aspects of SLE appear to be triggered by classic inflammatory mechanisms, accompanied by elevated acute phase reactants, and responsive to immunosuppres-sive therapies. Other aspects, such as those associated with antiphospholipid antibodies (aPL), are associated with hypercoagulability. Although inflammation contributes to these aspects as well, the approach to the treatment of aPL-mediated disease manifestations is usually centered on anticoagulation. Autoantibodies can occur in the absence of clinical features of SLE, but strong evidence implicates certain autoantibodies in the mediation of tissue damage in the kidney and other organs. Genetics plays a significant role in SLE, but the disease is clearly polygenic, with multiple genetic risk factors contributing incrementally to the overall genetic risk. Environmental risk factors are also critical. Established environmental risk factors for the disease include hormones, ultraviolet light, the exposure to certain medications, and possibly dietary exposures and infectious agents.