This working paper is part of a larger research project entitled "The Socio-Economic Performance of Social Enterprises in the Field of Integration by Work" (PERSE). The whole PERSE Project is coordinated by Marthe Nyssens (CERISIS, Catholic University of Louvain, Belgium) and is financed by the Europe Commission. This particular paper focuses on social enterprises in Belgium. It describes their context, origin and evolution. The paper includes a substantial bibliography.