The subject of the paper is the development of suitable models for the process design and process control of molten carbonate fuel cell (MCFC) systems. In a first step, a rigorous dynamic, spatially distributed model of an MCFC is derived from first principles. As this model is too complex for most process control purposes, a reduced model is developed in the following. The reduced model is derived from the spatially distributed reference model of the cell by applying the Karhunen-Loeve-Galerkin procedure. The reduced model is of considerably lower order than the original one and requires much less computational time. The applicability of the reduced model to process control problems is demonstrated by using it in the framework of a state and parameter estimator. (C) 2004 Elsevier Ltd. All rights reserved.