This article presents a study of a multilingual research park at the University of Barcelona (Catalonia), where administrative staff, researchers and other members interact in a variety of languages. Focusing on the use of Catalan, Spanish, and English the study investigates whether all scientific tasks are carried out in English (the monoglot hypothesis regarding scientific language practices) or whether they are carried out in different languages depending on several variables (interlocutors, domains, etc.). An online questionnaire was sent to all members of the university research staff, and their responses provide evidence that English is the scientific lingua franca of the scientific park, but this does not mean that English has become the default language of the institution, but rather that the institution functions essentially on the basis of trilingualism. Two main factors can be singled out when trying to explain the organization of this plurilingual practice: the professional role of the PCB (Parc Cientific de Barcelona) staff, and the type of communicative activity, the latter being strongly influenced by the intended addressee. A cluster analysis of the research staff at the institution shows that there are four sociolinguistic profiles of researchers depending on their proficiency in different languages and their geographic origin. The final section argues that the processes of language change do not occur in a compact but rather in a domain-by-domain manner, according to complex balances that depend on the composition of each linguistic ecosystem.