There is substantial evidence to suggest that a sedentary lifestyle is associated with increased risk of disease and reduced functional capacity. Although it has been established that significant health benefits can be gained from moderate levels of regular physical activity for all ages, a significant proportion of the elderly population remain sedentary. Perhaps, the elderly population has the most to gain from adopting health-promoting behaviors such as exercise. This application adopts a social contextual, public health approach to identifying, initiating and maintaining levels of physical activity among sedentary elderly citizens in Portland, Oregon. A range of psychosocial variables will be operationalized in identifying predictors and correlates of exercise participation. Variables related to adherence and maintenance will be guided by Bandura's Social Cognitive Theory, and participants' readiness for exercise will be measured by State of Change (Transtheoretical) Model variables. Specifically, self-efficacy and social support will function as key theoretical constructs in the maintenance of exercise among elderly participants. The study will examine the homogeneity of individuals within exercise groups and the heterogeneity of exercise groups demarcated by neighborhood, as well as environmental and social influences enhancing or compromising healthy exercise behavior. The study will recruit 600 elderly citizens 65 through 75 years of age, from 60 neighborhoods in the Portland, Oregon metropolitan area, to receive either a 6-month walking program, or an information-only program. The two groups (300 walkers from 30 neighborhoods --- 10 per group --- and 300 sedentary residents) will be matched on demographic and ethnic characteristics. Follow-up assessments will be conducted at three and six months after program completion. This study is likely to lead to a greater understanding of the mediating variables influencing senior physical activity, and the feasibility of a low-cost community program for increasing exercise among elderly sedentary adults.