This contribution aims to answer the question what we know about social entrepreneurship by summarizing the current state of knowledge. It first provides a broad description of what social entrepreneurship is. Next, a conceptual overview is given of different perspectives on social entrepreneurship. More specifically, four schools of thought on social entrepreneurship are presented and a description is given of the defining characteristics that distinguish these schools from one another. Subsequently some of the main findings of empirical studies from each of the four schools are summarized and discussed.