Various food processes aim at controlling the content and distribution of water in solid foodstuffs (at a macroscopic and molecular level) in order to increase their stability and shelf-life. The objective is generally to reduce the availability of water for undesirable reactions or transfers. This can be achieved most notably through partial removal of water, addition of water activity lowering agents, or change in the state of water. The various physical, physico-chemicaI and bio-chemical phenomena (transfer, reactions, transformations, deformations...) induced by or accompanying the migration or phase change of water are defined in this paper as "water mediated phenomena", which may influence the evolution and further behaviour of the food material during the process. The objective of the present paper is to show how the increased understanding of water mediated phenomena makes it possible to improve process control and food quality. This is illustrated by the analysis of the four following examples: i) control of thawing phenomena or solute concentration in the food outer layer in osmotic dehydration and immersion freezing, related to the evolution of inner concentration gradients andlor crystallisation phenomena; ii) control of cracker colour and texture, related to water departure mechanisms and solute entrainment by water during baking; iii) control of oil absorption related to the creation of heterogenous porous structure and internal pressure evolution during frying and cooling. (Résumé d'auteur)