Universities are the main knowledge-producing institutions, combining learning and research activities. Companies, in turn, play a role in the application of knowledge. In between, we find university-industry collaborations assuming various forms and stretching across different areas. One of the areas in which this cooperation takes place is doctoral education. The aim of this article is to discuss the role played by doctoral students, through their research, in the enhancement of university-industry collaborations, as they can be a vehicle of connection between academia and companies, but also because they can positively influence knowledge transfer and knowledge sharing. The discussion is framed by public policy initiatives formally promoting relationships between universities and companies in Portugal. We analyse the factors that contribute to make doctoral students important actors in creating and strengthening the cooperation between universities and companies and assess how their role varies between the scientific and economic environments. Our analysis is based on a survey conducted with doctoral programme directors in Portugal during the 2016/2017 academic year. From the main findings of the research, we highlight that doctoral students' research is a central element in university-industry collaboration, including in knowledge transfer, and that the more diverse the role of universities and companies, the more heterogeneous and important is the role of doctoral students.