A fundamental goal of Land Use – Transport Interaction (LUTI) models is to capture the strong interplay between land use and transportation in metropolitan areas. Inherently, sector-specific models, transport and urban alike, cannot take this interaction into account and thus miss one side of the story. LUTI models aim to fill this gap, and ultimately to provide better decision helping tools for urban and regional long term planning. LUTI models first appeared in the 1960s. The complexity of LUTI models, combined with computational limitations at the time, caused a pause in their development. However, interest in LUTI models has risen again in the 1990s and their number and complexity have been growing steadily ever since. This goes hand in hand with increasing expectations from end users as well as with new theoretical developments and a drastic increase in computational capacities, the latter enabling for instance the development of micro-simulation models.While spatial economics models may be mathematically more complex to handle, due to the requirement of reaching an equilibrium for a complex set of parameters and equations, activity-based models usually have more parameters and larger data requirements for their instantiation. Besides these differences, all LUTI models share several needs, among which – like for most models in general – a need for calibration (parameter estimation) methods in order to instantiate them and for validation approaches in order to justify their operational capacity. Both of these, parameter estimation and model validation, are complex issues; in this document we focus on numerical/computational aspects. The survey reported here is motivated by our conviction that the high complexity of current LUTI models requires the best possible numerical tools for calibration and validation. Developing and applying these tools is the primary objective set by the CITiES project funded by the French ANR (Agence Nationale de la Recherche). A starting point of this endeavor is a survey of existing state of the art reported in the LUTI literature. This document describes the scope of this ongoing study and some intermediate conclusions.