Paper presented at the Joint Mexico-OECD Conference on International Public/private Partnerships for Innovation, 2-3 December 2002, Puerto Vallarta (México)This paper aims to analyse the dynamics of relationships between public and private sector in the context of S&T policies and to present some experiences of Public/private partnerships (PP/Ps) in relation to innovation policy. It also attempts an understanding of the forces and factors that explain the increase of collaboration between public and private sectors, and its growing relevance in the discourse of S&T policies. The argument I put forward is that the general emphasis on public-private collaboration in science, technology and innovation policies is not only the outcome of a process of changing rationales for policy intervention to cope with problems of efficiency and implementation of traditional policies (OECD, 2002b), but also the result of general factors such as: some concrete S&T policy legacies, the overall Spanish political context emphasis on consensus, the tradition of corporatist arrangements, and the general concern on Industry-Science Relationship (ISR) issues, such as technology transfer and R&D collaboration.