Internationalization is a key contemporary debate within Higher Education (HE). Many universities worldwide proclaim their "international" status, citing quantitative indicators, particularly international student and staff recruitment and outbound student mobility data to illustrate this. In this paper, we focus on the non-mobile majority of the academic community. We foreground internationalization at home (IaH) and the underlying social, academic and intercultural learning benefits of an internationalized university experience. We explore how IaH is understood and operationalized in two universities in the United Kingdom and Portugal via a multiple case study. Qualitative data from 12 stakeholder interviews are analysed, generating five themes about operational understandings and practices of IaH. Findings identify relevant explanatory factors that may assist other institutions to understand, enact and communicate about IaH. We highlight the need for further empirical research to provide insights into how this key dimension of internationalization is being operationalized across other European HE institutions.