Social innovation is on the rise as a mode of governance through which to address societal challenges. Seeking to empower SI initiatives, researchers and policy makers are concerned with the development of supportive "ecosystems". This concept usefully calls attention to the distributed nature of SI agency, but many questions remain on the kinds of network constellations involved. This contribution unpacks the "SI ecosystems" concept, specifying how the empowerment afforded through SI networks rests on (1) local embedding, (2) transnational connectivity and (3) discursive resonance. Charting the variety of network constellations as studied in an international comparison of 20 transnational SI networks, a typology of SI ecosystems is constructed. Distinguishing five SI ecosystem ideal-types ranging from loosely integrated and locally focused co-creation hubs to globally connected and widely resonating political movements, the typology informs a differentiated approach to their understanding and development.