Aggregate or societal aging, however, is a recent phenomenon — one that has arisen as a consequence of the sweeping demo graphic changes of the 20th century. The increases in longevity and declines in fertility of the last century have caused important shifts in the age structure of our population. The typical "age pyramid" of a developed country has become increasingly rec tangular with a shrinking base. In the United States, persons age 65 or older now comprise approximately 13 percent of the population, and this figure will increase in the near future. The pro portion of elderly will rise to about one in six or seven persons within 25 years, with increasing proportions of the elderly at the "oldest old" ages (i.e., 80 years and above). Globally, there will be nearly 1 billion elderly by the year 2025; this number will double to 2 billion by 2050.

Both at the micro- and aggregate levels, aging intersects with multiple dimensions of our individual and social lives as well as with the well-being of our societies as a whole. As we age, the full spectrum of activities and interactions in our daily lives evolve: our needs and contribtions to economic life, our social networks and connections, how we efine and strive for well-being, all
change. The process of aging is inherently multidimensional; it
generates a need for a correspondingly interdisciplinary
approach among practitioners and scholars. Institutional
boundaries, both administrative and substantive, are ob-
stacles to the kind of comprehensive re search and training
that are neeeded and that we must resolve collectively. This
initiative seeks to continue a process that will develop the
kind of cooperative structure that will allow us to work con-
structively to address the challenges of aging.