Water vapor sorption is the most fundamental aspect of wood-moisture relations. It is directly or indirectly related to the physical properties of wood and the onset of wood-damage mechanisms. While sorption properties of cellulosic materials have been utilized since antiquity, the time-dependent transition from one moisture content to another known as sorption kinetics has received much less attention. USDA Forest Service researchers recently explored kinetic models of water vapor sorption in wood that have been developed over the past century. When rigorously tested, none of the models could match kinetic data, nor could they account for all of the physical phenomena observed in the water vapor sorption process of wood. USDA Forest Service researchers concluded that new experimental techniques need to be developed to further advance our understanding of water in wood.