In current business practice, an integrated approach to business and IT is indispensable. In many enterprises, however, such an integrated view of the entire enterprise is still far from reality. To deal with these challenges, an integrated view of the enterprise is needed, enabling impact/change analysis covering all relevant aspects. This need sparked the development of the ArchiMate language, which was developed with the explicit intention of becoming an open standard, and as such has been designed such that it is extendable while still maintaining a clear and orthogonal structure. This article is concerned with documenting some of the key structures and design principles underlying the ArchiMate language. ArchiMate is designed as an architecture description language (ADL) for enterprise architectures. The authors will start by discussing the challenges facing the design of an architecture description language. Consequently we discuss how the design principles of the ArchiMate language aim to tackle these challenges. They then continue with a discussion of the modelling concepts needed. In this, we make a distinction between concepts needed to model domains in general, the modelling of dynamic systems, and the modelling of enterprise architectures.