Abstract: The Open Distributed Processing （ODP） aims to provide a consistent interface model for the distributed application programs to achieve portability, interoperatability and distribution transparency. ISO RM--ODP gives a framework of distributedsystems, and uses five viewpoints to abstract the ODP systems. It also proposes concepts and structuring rules of the corresponding viewpoint languages to specify the viewpoints. This paper introduces five viewpoints and the corresponding languages’ conceptsand structuring rules. The relationship between the viewpoint languages is also discussed.