The article aims to describe and analyse the opinions of European physicists as to the reasons for the overrepresentation of men in the discipline, as well as to supply some reflections on the barriers encountered by female physicists in their careers. The article is based on qualitative data – 83 in-depth interviews with female and male physicists – collected in 2016 and 2017 under the framework of the project “Gender Equality Network in European Research Area” (GENERA). The main reasons voiced by interviewees for the gender imbalance in physics are to be found ‘outside’ the scientific institutions themselves, namely the early processes of the socialisation of girls and boys, together with existing gender stereotypes. Other reasons are related to recent developments in academia linked to work organization and structural conditions – precariousness, competitiveness, and the demand for mobility, but also to a masculinised working culture resulting in gender bias, as well as microaggressions and discrimination. In relation to recent studies showing that awareness of gender (in)equalities remains of crucial importance for structural/institutional change, the article reflects on the potential implications of the perception by physicists of the determinants of gender inequality for the implementation of gender equality policy in research organisations.