Abstract: Although it originated as a language for software modeling, the Unified Modeling Language (UML) is increasingly used for conceptual modeling of application domains. However, due to its origins, UML has many constructs that are purely software oriented. Consequently, it might not be suitable for modeling “real world” phenomena. This chapter aims to assign real-world semantics to a core set of UML constructs. We propose principles for mapping UML constructs to the formal ontology of Mario Bunge, which has been widely used in information systems modeling contexts. We conclude by outlining how the proposed principles can be evaluated empirically in terms of their effectiveness in supporting conceptual modeling using UML.