This study analyses whether CERN researchers show an entrepreneurial behaviour both at the personal and at organizational level and what are the factors related to such behaviour. Entrepreneurship is here defined as the interest of the researchers to collaborate with industry in the widest sense, for example filing patents or copyrights, interacting with the industrial and commercial sector for the development of machines or transferring know-how, etc. Factors influencing a researcher''s entrepreneurial behaviour have been identified and categorized. The main questions addressed by the study were: Have CERN''s researchers become (more) entrepreneurial after the introduction of a formal Technology Transfer policy at CERN in 1988, other things being equal? Are there incentives that (can) play a role in encouraging CERN''s researchers to become (more) entrepreneurial? Has there been a shift in research interests of CERN''s researchers toward also more applicable research results? Practically, are entrepreneurship and scientific research considered complementary or substitutive activities at the level of the individual researcher?