Two hundred and twenty five healthy, sedentary men and women ages 55 and older will be randomly assigned to one of three conditions: 12 months of physical activity counseling delivered by a human counselor, 12 months of physical activity counseling delivered by a telephone-linked computer system, or a 12-month attention-control condition (a health education class). Data on physical activity participation and related quality of life indicators (e.g., improved physical functioning, fitness, sleep) will be collected at baseline, 6 months, 12 month post-test and 18 month follow-up. The primary hypotheses are: