The analysis of how research contributes to society typically focuses on the study of those transactions that are mediated through formal legal instruments (research contracts, patent licensing and the creation of companies). Research has shown, however, that informal means of technology transfer are also important. This paper explores the importance of informal collaborations and provides evidence of the extent to which informal collaborations between researchers and non-academic partners take place informally in the social sciences and humanities (SSH). Data is obtained from two studies on knowledge exchange involving researchers working in the SSH area of the Spanish Council for Scientific Research. We show that informal collaborations not officially recorded by the organisation are much more common than formal agreements and that many collaborations remain informal over time. We explore the causes of such prevalence of informality and discuss its policy implications.