Community level projects play a vital role in sustainability transitions. Be it the planning of a heat network, liberating a neighborhood from transit traffic, or a collective investment in home improvement, social dynamics often determine the success or failure of an innovative community project. The EU SMARTEES project studied social dynamics of innovation in five types of energy- and mobility-related local social innovations in ten front-runner cities and islands across Europe. These case studies provided rich data and fascinating stories on the complexities of social innovation. Computational social simulation models were developed for a variety of cases, allowing for experimentation based on the modelling of actual community behavior, with different interests, positions and social networks represented through the diverse case selection. The results of these experiments and the robust research done in SMARTEES are captured in an innovative “Policy Sandbox-tool” that allows planners working with social innovation testing out different scenarios, to help determine the best course of action. During the SMARTEES conference, attendees will be able to explore the tool and learn about state of the art insights on how to support communities and strengthen local democracy to achieve sustainable energy- and mobility transitions.