Semantic Mining of Activity, Social, and Health data (SMASH) is a multiple-discipline research among computer scientists, medical doctors, and social scientists. Traditionally, support groups and other social reinforcement approaches have been popular and effective in dealing with unhealthy behaviors including overweight. Research in the design and implementation of the SMASH (Semantic Mining of Activity, Social, and Health data) system will address a critical need for formal ontologies and data mining tools to help understanding the influence of healthcare social networks, such as YesiWell, on sustained weight loss where the data are multi-dimensional, temporal, semantically heterogeneous, and very sensitive. SMASH will develop new methods in social network analysis, Semantic Web ontologies, privacy preserving data mining, building on the current state-of-the-art. This project is being supported with a three-year R01 grant by the NIH/NIGMS.