In recent years, it has become common to highlight the positive aspects of ‘‘successful aging.’’ Both popular and scholarly reports emphasize pathways to optimal health, well-being, social integration, and life satisfaction in later years. Indeed, it is the case that some individuals retain high physical and mental function into very advanced old age. However, it is also unfortunately true that many people spend the final years of their lives with serious limitations resulting from chronic illness or disability. Although many Americans are living longer and healthier than ever before, the risk of chronic disease increases dramatically with age (Jette, 1996; Manton, 1996). The strong correlation between advanced age and the incidence of cognitive impairment, as well as the prevalence of psychiatric disorders (cf., Roberts, Kaplan, Shema, & Strawbridge, 1997), suggests that hazards to mental health are also tied to the aging process. Further, negative life transitions such as widowhood, loss of meaningful roles, and admission to a nursing home are likely to occur in old age. These transitions often lead to social isolation and decreased well-being. (Pillemer, Moen, Wethington, & Glasgow, 2000). The dichotomy between the ideal of optimal physical and mental functioning and the unfortunate reality of the vulnerability that many older people face has provided the impetus for a strong applied focus in the field of gerontology. Gerontology, like psychology (Izard, 2002), has from its beginnings comprised both a science and a profession. Unlike other disciplines in which the researcher–practitioner relationship has been characterized by animosity (Gillan & Schvaneveldt, 1999; Weisz, Donenberg, Han, & Weiss, 1995), there is a tradition within gerontology of communication and cross-fertilization between the scientific and practice communities. Throughout its history, gerontology has grappled with applied and practical questions, such as How can the lives of older persons be improved? What services and resources work well to solve the problems experienced by older individuals and their families? and What strategies are best for promoting independence, reducing physical vulnerability, and easing psychological distress? In an attempt to answer these questions over the past half century, a vast array of programs has been developed to moderate the negative effects of aging and to foster individuals’ adaptation to inevitable age-related changes in function. In concert with such efforts, gerontologists have experimented with changing the structure of tasks and activities and the contexts and environments in which older people live, including families, housing arrangements, and communities. Despite the limited evidence of animosity between gerontological researchers and practitioners, the connection between research and application still leaves much to be desired. Although social scientists are fond of quoting Kurt Lewin’s famous dictum that there ‘‘is nothing so practical as a good theory,’’ relatively few have attempted to translate their theories into actual practice. Similarly, there is generally a failure to use research results to guide the design of social interventions and programs (Levy-Leboyer, 1988). Within this context, it is not surprising that there has been a call for more rigorous, research-based approaches to intervention development (Ory, 2000; Schulz, Maddox, & Lawton, 1998). To put it simply, with the aging of the population, it is more important than ever to know what works, why it works, and with whom it works best. Address correspondence to Karl Pillemer, Cornell Gerontology Research Institute and Department of Human Development, MVR G44, Cornell University, Ithaca, NY 14853. Email: kap6@cornell.edu Cornell Gerontology Research Institute and Department of Human Development, Ithaca, NY. University of Miami School of Medicine, Department of Psychiatry and Behavioral Sciences, Center on Adult Development and Aging, Miami, FL. Department of Psychiatry and University Center for Social and Urban Research, University of Pittsburgh, PA. Behavioral and Social Research Program, National Institute on Aging, National Institutes of Health, Bethesda, MD.