Transformative social innovation can play a critical role in shaping the direction of sustainability transitions. In this report, we conceptualise social innovations as (combinations of) ideas, objects, and/or activities that alter social relations and introduce new ways of doing, thinking, and organising. We consider social innovations to be transformative to the extent that they challenge, alter, and/or replace dominant institutions (Avelino et al., 2019). This report explores six cases of transformative social innovation (TSI) to better understand its potential and role in sustainability transitions, as well as implications for governance, finance, and impact measurement. We discuss how each of these cases is related to distinct change logics, i.e. how they respond to failures in production and consumption systems, as well as their emergence and diffusion, transformative potential, and possible drawbacks. The cases relate to car sharing, repair cafes, credit unions, slow food, collaborative housing, and participatory budgeting. Taking stock of the analyses of these cases, we posit five insights on: 1) Cultivating social innovation ecosystems: Recognising how the transformative potential of TSI depends on ecosystems —meaning the degree to which roles, functions, structures, and norms are enabling or impeding. 2) Measuring impact: Acknowledging that social innovations yield outcomes that can be difficult to track, which necessitates a nuanced understanding of their impacts. 3) Developing resourcing and finance mechanisms: Emphasising the need for innovative financial structures to support and sustain social innovation. 4) Navigating mainstreaming and co-optation dynamics: Identifying the delicate balance between social innovations reproducing and disrupting production and consumption systems in order have transformative impact. 5) Understanding the limits of social innovation: Recognising that while social innovation holds great potential, it is not a panacea and can have drawbacks. In conclusion, this report provides insights to guide the development of governance to support the emergence and diffusion of social innovation toward facilitating transformations of production-consumption systems, for achieving just and sustainable systems.