Cataract disrupts the crystalline lens, a transparent, elastic, avascular, biconvex structure composed of a capsule, lens epithelium, and lens fiber cells. Many factors contribute to the progression of lens opacity, but aging is most frequently associated with cataract. As aging-related cataract develops, many biochemical and biophysical changes occur, most notably a marked increase in the insolubilization of the crystallin and extensive oxidation damage to many of the lens constituents. Cataract management should include ophthalmologic history and examination, medical evaluation, optical correction, control of ocular and systemic disease that may contribute to cataract, discontinuation of cataractogenic drugs, and periodic reexamination. Surgery is indicated when cataract is associated with vision decrease interfering with activities important to the patient, intraocular inflammation or glaucoma, or interference with management of posterior segment disease. More than 600 000 cataract operations are done in the United States each year; in 1982 an estimated 496 000 cataract operations were combined with intraocular lens implantation.