In the environmental domain there are a multitude of existing legacy models and statistical procedures that have to be integrated in modern environmental information systems being Web-based or realized as classical client/server applications. The ORCHESTRA project provides an architectural framework and a set of services that allows to build service networks based on international standards of ISO, OGC, W3C and OASIS. In this book the design of an application and a service network, that allows users to discover and invoke environmental models, is described. As a baseline, the existing ORCHESTRA services, especially the ORCHESTRA Catalogue Service, are integrated in architecture. The design of the service network describes the used services and the workflow, which is required to find and invoke the required environmental model. Furthermore a possible design and implementation of a client application is specified. For this application a search interface, which allows the user to build extended search queries in an easy way, is designed and implemented. The used enviromental model is SIMIK+. It is a spatial interpolation model for chemical contamination of ground water.