Innovation is sometimes the result of collaboration between different agents with complementary resources. When companies make formal agreements to collaborate in R&D they do so with different types of organizations, such as their competitors, suppliers, and customers, or universities and research centres. This paper focuses on attempting to understand the reasons that lead companies to cooperate with universities and research centres and the characteristics of the relationship that this involves. The empirical study is based on a sample of 747 Spanish firms that took part in some type of collaborative R&D project between 1994 and 1996. Results indicate that cooperation with centres is a nation-wide phenomenon involving basic research, conducted under the sponsorship of different research support schemes promoted by central and regional administrations.