Requirements engineering is an important and complex phase during systems development because it combines the description of the system’s domain with the elicitation, specification and validation of application-specific requirements. In this paper we propose an ontology-based requirements engineering approach that integrates the use of domain ontologies to capture domain knowledge into early requirements modelling techniques, which primarily aim at eliciting and representing the organisational and intentional context of the system. The proposed approach can be used with different types of domain ontologies and different requirements engineering techniques. The approach is illustrated using the REA enterprise ontology, the E³-value ontology and the i* requirements modelling framework.