Requirements engineering (RE) encompasses a set of activities for eliciting, modelling, agreeing, communicat- ing and validating requirements that precisely define the problem domain for a software system. Several tools and methods exist to perform each of these activities, but they mainly remain separate, making it difficult to capture the global consistency of large requirement documents. In this paper we introduce model-driven engineering (MDE) as a possible technical solution to integrate these activities in a common framework. First, we dicuss how RE can lever- age the two main techniques for MDE: metamodelling and model transformation. Then, we introduce a metamodel for requirements and present how we have implemented this metamodel to make it executable and usable through a con- strained natural language for requirements definition.