In model-driven engineering approaches, models are considered firstclass entities. The composition of models is a necessity for modelling software systems. Structural composition of models has been studied thoroughly during the course of the last decade. However, composition or integration of executable models’ operational semantics is still an open problem. In this report we propose a mechanism for integrating the operational semantics of programming languages. The mechanism is highly flexible and provides the developers with a powerful tool for adapting languages for a specific software development project. Importantly, integration of operational semantics can be achieved without breaking the conformance between existing models and their metamodel whose operational semantics is integrated with the operational semantics of another metamodel.