Volume 39 of Reviews in Mineralogy and Geochemistry about Transformation Processes in Minerals summarises the current state of the art. The selection of transformation processes covered here is by no means comprehensive, but represents a coherent view of some of the most important processes which occur specifically in minerals. Contents: Rigid unit modes in framework structuresStrain and elasticity at structural phase transitions in mineralsMesoscopic twin patterns in ferroelastic and co-elastic mineralsHigh-pressure structural phase transitionsOrder-disorder phase transitionsPhase transformations induced by solid solutionMagnetic transitions in mineralsNMR spectroscopy of phase transitions in mineralsInsights into phase transformations from M ssbauer spectroscopyHard mode spectroscopy of phase transitionsSynchrotron studies of phase transformationsRadiation-induced amorphization