The issues of linking single process models with TIS have been well rehearsed. Linking several models raises some new issues. Rewriting the logic and relationships of existing models into one large model cannot always be justified. An alternative approach is to construct links from a GIS to the models using a network of programs and structures. Issues of this approach are: a) reconciling the representations of reality used by the models and the GIS; b) simulating the interactions between the subsystems by controlling the flow of data between different models; c) constraints such as the system resources, user expertise and model limitations; d) coping with data requirements and with error and; e) fusion of models and data with different scale properties. This paper describes how these issues are being addressed for a project where several process models are being applied to simulate the agricultural effects of water table drawdown.