In enterprise architecture, the goal is to integrate business resources and IT resources in order to improve an enterprises competitiveness. In an enterprise architecture project, the development team usually constructs a model that represents the enterprise: the enterprise model. In this paper, we present a modeling language for building such enterprise models. Our enterprise models are hierarchical object-oriented representations of the enterprises. This paper presents the foundations of our language (i.e. the Living System Theory and the RM-ODP standard), the definition of the language and ends by presenting an example of an enterprise model developed with our web-based CAD tool.