The use of model-based methods to support planning, designing, and operating chemical processes and plants has recently gained an increased importance in the daily work of process engineers. The development of mathematical models through the use of standard flow sheet simulation tools requires the expertise of an experienced designer. Therefore, the value of existing models is not limited to the resources required for their development, but also includes value in the form of knowledge about an enterprise's products and production processes. The reuse of existing models and design experiences in order to lower the costs of model development is therefore economically desirable. This report gives an overview of the systematic long-term management and use of mathematical models., Some motivating scenarios are used to derive the requirements for a model management system and to evaluate existing methods and tools. The results of these example scenarios are then used to guide the development of a model management system. After presenting a prototypical implementation the article concludes with an outlook on the future importance of model management systems.