Many countries have amended legislation and introduced policies to stimulate universities to transfer their knowledge to society. The effects of these policies on scientists are relatively unexplored. We employ principal–agent theory to increase our understanding of the relationship between impact policies and scientific practice. Our methodology includes the analysis of policy documents and of data gathered in focus groups. We conclude that there is a gap between policy on the one hand and how scientists perceive it on the other. Policy documents put forward a broad notion of impact, but scientists perceive them as focusing too narrowly on commercial impacts. Scientists are further puzzled by how societal impact is evaluated and organised, and their perceptions frame their behaviour. Our policy recommendations focus on improving the interaction between intermediaries, such as universities and research councils, and scientists so as to include the latter’s perspective in policy-making.