This paper reviews and discusses the emergent entrepreneurial ecosystem approach. Entrepreneurial ecosystems are defined as a set of interdependent actors and factors coordinated in such a way that they enable productive entrepreneurship within a particular territory. The purpose of this paper is to critically investigate the emerging literature on entrepreneurial ecosystems. Current work on ecosystems is underdeveloped, focusing more on superficial generalizations based on successful case studies such as Silicon Valley or Boulder, Colorado rather than on rigorous social science research. The paper provides a review of the multiple definitions of ecosystems found within the literature, and discusses the relationships between ecosystems and allied concepts such as industrial districts, clusters, and innovation systems. The paper concludes by discussing an integrative model that connects the functional attributes of entrepreneurial ecosystems (including framework conditions and systemic conditions) with entrepreneurial outputs and welfare outcomes. The framework conditions consist of the social (informal and formal institutions) and physical conditions enabling or constraining human interaction. Systemic conditions are the heart of the ecosystem and include networks of entrepreneurs, leadership, finance, talent, knowledge, and support services.