Produced as part of the OECD Global Action on Promoting Social and Solidarity Economy Ecosystems, funded by the European Union’s Foreign Partnership Instrument, this paper provides a framework to clarify the core notions of the social and solidarity economy, along with social economy, social enterprise, social innovation and other related notions. The objective is to explain what they are and understand how these notions have evolved in recent decades. It also aims to capture and document the great diversity within social and solidarity economy organisations in terms of purposes, legal entities, business models and practices to help better characterise the “population” of social and solidarity economy entities.