Late-life disability has been declining in the United States since the 1980s. This study provides the first comprehensive investigation into the reasons for this trend. The study draws on evidence from two sources: original data analyses and reviews of existing studies. The original analyses include trend models of data on the need for help with daily activities and self-reported causes of such limitations for the population aged seventy and older, based on the National Health Interview Surveys from 1982 to 2005. Increases in the use of assistive and mainstream technologies likely have been important, as have declines in heart and circulatory conditions, vision, and musculoskeletal conditions as reported causes of disability. The timing of the improvements in these conditions corresponds to the expansion in medical procedures and pharmacologic treatment for cardiovascular disease, increases in cataract surgery, increases in knee and joint replacements, and expansion of medications for arthritic and rheumatic conditions. Greater educational attainment, declines in poverty, and declines in widowhood also appear to have contributed. Changes in smoking behavior, the population's racial/ethnic composition, the proportion of foreign born, and several specific conditions were eliminated as probable causes. The substantial reductions in old-age disability between the early 1980s and early 2000s are likely due to advances in medical care as well as changes in socioeconomic factors. More research is needed on the influence of health behaviors, the environment, and early- and midlife factors on trends in late-life disability.