Planning support systems (PSS) are computer-based geo-information instruments incorporating components that planners can utilize to explore and manage their activities. Independent of this, there are computer models designed to anticipate scenarios of spatial urban development under certain policy assumptions. These so-called land-use transport interaction (LUTI) models integrate developments in demography, economy, land use, transport and environment, and the interactions between them over spatial scales and time. They are typically highly complex and require large data sets and long computing times. This reduces their role as planning support tools, but reinforces their role of generating knowledge for better understanding and communicating the long-term future of cities. This chapter gives an overview about the growing range of subject areas, methods and policy fields addressed in current LUTI models and explains under what conditions LUTI models can be called PSS.