David Gershon discusses the role of social networks as game changers in efforts to bring about social change. Gershon presents some of the results of his research looking at the effectiveness of different types of social networks in encouraging and sustaining group participation. Gershon asserts that neighborhood groups are a particularly effective form of organization for instigating social change. Presented at the Garrison Institute’s Climate, Buildings and Behavior Symposium, May 2010.