Shrinkage of foodstuffs is a common physical phenomenon observed during different dehydration processes. These changes affect the quality of the dehydrated product and should be taken into consideration when predicting moisture and temperature profiles in the dried material. The aim of this work is to give a physical description of the shrinkage mechanism and present a classification of the different models proposed to describe this behaviour in food materials undergoing dehydration. The models were classified in two main groups: empirical and fundamental models. Empirical models are obtained by means of regression analysis of shrinkage data. Fundamental models are based on a physical interpretation of the structure of food materials and try to predict dimensional changes due to volume variation of the different phases in the food system along the drying process. Several models referred to in this work were compared with experimental data on air drying of apple, carrot, potato and squid flesh. Average relative deviations between experimental and predicted values of shrinkage found were in most cases less than 10%. For some materials, models that neglect porosity change tend to show larger deviations. (C) 2003 Elsevier Ltd. All rights reserved.