Under-contribution is a problem for many online communities. Social psychology theories of social loafing and goal setting can provide mid-level design principles to address this problem. We tested the design principles in two field experiments. In one, members of an online movie recommender community were reminded of the uniqueness of their contributions and the benefits that follow from them. In the second, they were given a range of individual or group goals for contribution. As predicted by theory, individuals contributed when they were reminded of their uniqueness and when they were given specific and challenging goals, but other predictions were not borne out. We are conducting further experiments to clarify the surprising findings. • Project Members: Dan Cosley, Dan Frankowski, Robert Kraut, Al Mamunur Rashid, Paul Resnick, Loren Terveen • Papers resulting from this project