This paper questions the widespread tendency to view academic spin-outs as an undifferentiated category and explores typologies of companies originating in universities, using a Penrosean conceptualization of entrepreneurial activity. We initially identified five main types of business activities pursued by academic entrepreneurs, which we revised after analyzing a database of Cambridge University spin-outs and real-time exemplars of emerging ventures. The refined typology takes into account the dynamic of the entrepreneurial process. As the business models of ventures evolve they may enter a different category of business activity. We conclude by discussing the academic and practical needs for a better understanding of the heterogeneity of spin-outs, the diversity of which has theoretical and policy implications.