Throughout the world all populations are seeing burgeoning numbers of "elders", defined as persons aged 65 year and older. In many countries, including Japan, the United States, Norway, Sweden and the United Kingdom, those aged over 65 are at or approaching 15% of the population. As their numbers have increased, so have their health care expenses, leading to extensive research on the health, well being, and life expectancy of these increasingly older elders. Today this group is further sub-divided: the young-old ages 65-74, the old-old ages 75-84, and the oldest-old ages 85+, for both health care and research purposes. However broad variation still characterizes even these groupings. Rates of frailty and disability increase with increasing age among these elders. For example, inabilities to complete at least one activity of daily living increased from about 5-7% at ages 65-69 years to about 28-36% at ages 85+ in 1987. Death rates continue to decline at all ages past 50 years and rates of disability seem to be doing the same. For the foreseeable future, we may expect increasing numbers of older, frail elders than in previous decades. Thus, people are not only living longer, they generally are healthier at advanced ages than were previous cohorts, thus "old age" disabilities of the 20th century will be put off to even older ages during the 21st century. As yet there is no clear way to assess senescent changes in humans, although activities of daily living, allostatic load, and frailty indices have all been suggested. One future need is greater development and use of universal and accessible design in all aspects of the built environment.