Small farms dominate the European agricultural landscape, but they are much less represented in agricultural decision-making structures than larger farms. The weak political representation of small farms diminishes the degree to which their needs are addressed in public agricultural policies and support measures. This underrepresentation has been constraining small farms' contribution to food and nutrition security and sustainability. This paper explores the science – policy interface as boundary networks between researchers and policy-makers, to generate policies that are better-informed and better tailored to small farms' situations. It gathers researchers' experiences, from the Horizon 2020 project SALSA, through a range of project-generated activities and knowledge, of their engagement in the policy process. From the case studies analyzed, three types of SPI emerge: expert advice, networking platform and collaborative governance. Cooperation between researchers and policy-makers, that is often embedded in broader stakeholders’ networks, generate three kinds of contributions: better-informed policy process; increased social capital and empowerment of participants; and improved participant knowledge and skills.