Social innovation is presented as a viable alternative to incite systemic changes related to sustainability in its three dimensions (social, environmental and economic), to involve the government, companies and, above all, civil society. In order to understand the development of social innovation in Brazil and Portugal, and to promote cross-sector collaboration, we have conducted several case studies involving centers for social innovation in both countries. The data analysis demonstrates that collaboration between sectors and the construction of collaborative networks is as a key element in the development and sustainability of social innovation. In spite of this, in practice the construction of these networks is not trivial, there is the need to manage these networks innovatively. The literature review points out the key enablers for cross-sector collaboration in the context of social innovation, the alignment of values and goals, mutual trust, commitment and bridge leadership.