The commercial exploitation of new knowledge created in universities has become increasingly important to universities and to the governments that fund university research. One of the key avenues through which commercialisation occurs is the spin-off of new venture companies, often headed by faculty or staff of the originating university. It is interesting to note, however, the degree to which universities differ in their spin-off activity across different institutional contexts. The importance of this topic to policy makers is reflected in a rapid increase in the number of journal publications that seek to explain this variation in spin-off activity and that suggest policies that would increase this activity. In this paper, we review the academic entrepreneurship literature to identify the determinants of spin-off activity in universities. We suggest that the literature can be categorised into six separate streams. We then outline the limitations of existing research. We seek to synthesise existing research by presenting a framework that captures the determinants and consequences of spin-off activity.