Physical inactivity is a major cause of disease in the United States and globally. Effective physical activity interventions often use community based approaches due to the demonstrated effectiveness of combining individual and group based behavioral strategies towards encouraging physical activity behaviors and influencing social norms. Such interventions can increase their impact by adopting technology based solutions to facilitate the underlying behavioral strategies. Current technologies for persuading physical activity primarily focus on facilitating the individual level behavioral strategies and de-emphasize the interpersonal aspects. This dissertation focuses on the development and evaluation of technology that is aimed at facilitating group dynamics-based strategies for promoting physical activity within small socially connected teams. This dissertation introduces a multi-component smartwatch-centered system (FitAware) that uses sensors to automatically track physical activity and leverages the advantages of the watch form factor to facilitate both group and individual level behavioral strategies via non-interruptive, glanceable, and frequent feedback updates. This manuscript describes the design and evaluation of FitAware in the context of an 8 week statewide physical activity community-based intervention, culminating in guidelines for system development that have been tested in educational settings. / Ph. D. / Physical inactivity is a major cause of disease around the world. A good way to tackle this challenge is to conduct community-based physical activity interventions because of their effectiveness in the use of both individual and social approaches for influencing behaviors. An important challenge with such interventions is increasing their impact on the communities. Mobile technology can be used as a platform that can help reach more people. Mainstream devices for promoting physical activity focus on facilitating individual level behavioral strategies (e.g., how many steps one walked) and de-emphasize the interpersonal aspects (e.g., how ones steps compare to friend’s steps) which makes them less than optimal for facilitating the social approaches within community interventions. This dissertation focuses on the design, development and evaluation of a system that prioritizes both individual and interpersonal behavioral strategies for promoting physical activity. This work introduces a multi-component smartwatch-centered system (FitAware) that uses sensors to automatically track physical activity and leverages the convenience of the wristwatch information accessibility to facilitate both group and individual level behavioral strategies via non-interruptive, glanceable, and frequent feedback updates. This dissertation describes the design and evaluation of FitAware as part of an 8 week statewide physical activity community-based intervention, culminating in guidelines for system development that have been tested in educational settings.