In this report, a conceptual framework is presented to conduct an ex-ante impact assessment for social innovation. The building blocks for an ex-ante impact assessment are goal formulation; developing the relationships between inputs, outputs and outcomes; determining the role of stakeholders to achieve the objectives; calculating the impact; and deciding on the social innovation. These building blocks are sequentially interconnected to each other. In conclusion, our conceptual framework aims to be a practical guide to both assessor and assessee by structuring the development and decision process. A toolbox has been developed, which consists of a series of steps sprung from our conceptual framework.