Pressure-solution and associated crystallization are subclasses of a diffusive mass transport process which involves diffusion in grain boundary and pore solutions. The manner in which they give rise to permanent deformation is examined in three steps: (a) A simplified reversible non-hydrostatic crystal-solution thermodynamic criterion (first order, 2-components) based on Gibbs provides a manageable basis for determining the direction in which the process will run (regions of dissolution or growth) in stressed porous, non-porous, closed and open systems. (b) Considerations of irreversible diffusion and deformation indicate certain restrictions on the displacements accompanying permanent growth or dissolution and hence on the form of the solution-transfer strain rate tensor. (c) The way in which the process develops, and its rate, are governed by kinetic factors, especially diffusion kinetics. As well as having an exponential dependence on stress, the displacement rate is influenced by absolute temperature, grain boundary diffusivity, initial solubility and geometric scale.