This paper focuses on the process of multilingual concept scheme construction and the challenges involved. The paper addresses concrete challenges faced in the construction process and especially those related to equivalence between terms and concepts. The paper also briefly outlines the translation strategies developed during the process of concept scheme construction.<p>The analysis is based on experience acquired during the establishment of the Finnish thesaurus and ontology service Finto as well as the trilingual General Finnish Ontology YSO, both of which are being maintained and further developed at the National Library of Finland. </p><p>Although URIs can be considered language-independent, they do not render concept schemes and their construction free of language-related challenges. The fundamental issue with all the challenges faced is how to maintain consistency and predictability when the nature of language requires each concept to be treated individually. The key to such challenges is to recognise the function of the vocabulary and the needs of its intended users.</p><p> Open science increases the transparency of not only research products, but also metadata tools. Gaining a deeper understanding of the challenges involved in their construction is important for a great variety of users – e.g., indexers, vocabulary builders and information seekers. Today, multilingualism is an essential aspect at both the national and international information society level. </p><p>This paper draws on the practical challenges faced in concept scheme construction in a trilingual environment, with a focus on “concept scheme” as a translation and mapping unit.</p>