Recent European research has revealed growth in the number of administrators and professionals across different sections of universities-a long established trend in US universities. We build on this research by investigating the factors associated with variation in the proportion of administrators across 761 Higher Education Institutions (HEIs) in 11 European countries. We argue that the enactment of expanded and diversified missions of HE is one of the main factors nurturing universities' profesional and administrative bodies. Our findings support such an assertion; regardless of geographical and institutional differences, HEIs with high levels of "entrepreneurialism" (e.g. in service provision and external engagement) are characterized by a larger proportion of administrative staff. However, we find no empirical support for arguments citing structural pressures and demands on HEIs due to higher student enrolments, budget cuts or deregulation as engines driving such change. Instead, our results point towards, as argued by neo-institutionalists, the diffusion of formal organization as a model of institutional identity and purpose, which is especially prevalent at high levels of external connectedness.Keywords Higher education . Professional and administrative staff . Organizational expansion . Functionalism . Neo-institutionalism . EntrepreneurialismThe last couple of decades have marked a shift in the very nature of higher education (HE) as a knowledge institution. The early nineteenth century Humboldtian model of an elite institution prioritizing the pursuit of knowledge on its own left its place to the late twentieth century myth of the knowledge society (Meyer et al. 2006). Higher education institutions (HEIs) are facing High Educ (2018) 76:213-229 https://doi.