A Process Support System provides the tools and mechanisms necessary to define, implement and control processes, i.e., complex sequences of program invocations and data exchanges. Due to the generality of the notion of process and the high demand for the functionality they provide, process support systems are starting to be used in a variety of application areas, from business re-engineering to experiment management. In particular, recent results have shown the advantages of using such systems in scientific applications and the work reported in this paper is to be interpreted as one more step in that direction. The paper describes Geo-Opera, a process support system tailored to spatial modeling and GIS engineering. Geo-Opera facilitates the task of coordinating and managing the development and execution of large, computer-based geographic models. It provides a flexible environment for experiment management, incorporating many characteristics of workflow management systems as well as a simple but expressive process modeling language, exception handling, and data and metadata indexing and querying capabilities.