Model re-use is one of the old challenges in modeling and simulation. Already the syntactic exchange of models provide a lot of challenges -- however when it comes to semantic issues we are facing some unsolved problems. The course will give an overview about describing models and data at meta level, standards for exchanging models (in modeling and simulation in general), and in Systems Biology in particular. About techniques such as XML and OWL, and how they fit into this scheme, about ontologies and what possible role they play. Particularly, model composition by third party users requires a good understanding not only of syntactical issues but also the semantics of models.