To test this hypothesis, we will conduct a clinical trial that compares the enhanced intervention (story-based video games) to a standard intervention in 90 sedentary, overweight postmenopausal breast cancer survivors. Participants in the enhanced group will receive a mobile device and accessories with two story-based video game applications installed. The games incorporate behavior change strategies such as self-monitoring and feedback while also using game mechanics and a lengthy storyline to motivate physical activity. Participants in the standard group will receive the same mobile device with an electronic activity monitor and its companion feedback application. Both groups will receive brief weekly telephone counseling. By comparing two groups that both receive typical behavior change intervention components (counseling) and a novel electronic intervention, we will be able to investigate the specific effects of game mechanics and storytelling on motivation and physical activity. We will measure changes in physical activity, fitness, function, and quality of life from the beginning of the study to 6 months. We will also investigate further changes during an additional 6 month follow-up period in which participants keep their intervention tools but do not receive any counseling, to measure maintenance of activity. This project will develop and test a promising, innovative intervention that has the potential to be used on a widespread basis in clinical and community settings.