Organizations increasingly rely on external sources of innovation via inter-organizational network relationships. This paper explores the diffusion and characteristics of collaborative relationships between universities and industry, and develops a research agenda informed by an 'open innovation' perspective. A framework is proposed, distinguishing university-industry relationships from other mechanisms such as technology transfer or human mobility. On the basis of the existing body of research, the role of practices such as collaborative research, university-industry research centres, contract research and academic consulting is analysed. The evidence suggests that such university-industry relationships are widely practised, whereby differences exist across industries and scientific disciplines. While most existing research focuses on the effects of university-industry links on innovation-specific variables such as patents or firm innovativeness, the organizational dynamics of these relationships remain under-researched. A detailed research agenda addresses research needs in two main areas: search and match processes between universities and firms, and the organization and management of collaborative relationships.