This review examines the chemical and physical factors that control the response of silica gel to stimuli such as aging, heating, mechanical deformation, and drying. When the liquid phase is chemically aggressive, the gel exhibits spontaneous shrinkage (syneresis) and viscoelasticity; in an inert medium, the network of the gel is purely elastic. The rate of the responses to mechanical loads and changes in temperature depends on the permeability, as well as the modulus, of the network. The properties of the gel change by orders of magnitude as the network contracts during drying, and this has a dramatic effect on the drying stresses.