There is recently great progress in the understanding of the mechanisms behind metamorphic processes and the rates at which they perform. One reason lies the advancement in experimental techniques and microanalytical capabilities that allow chemical and structural analysis on ever smaller scale. This development is paralleled by the advent of theoretical tools that clear the way for a realistic computation of complex reaction and deformation processes in multicomponent systems. It has become feasible to combine the driving forces determined by thermodynamics (phase equilibria, phase transitions) and rheology (chemical-mechanical feedback) with reaction kinetics (e.g. diffusion, nucleation, crystal growth) in a way applicable to natural rocks. Examples include texture evolution, chemical and isotopical zoning in crystals and the migration and chemical nature of grain boundaries. Due to computational opportunities, insight on small-scale is now with high resolution applied to big-scale metamorphic processes in the broadest sense (e.g. tectonics, chemical mass transport in crust and mantle). Contributions are welcome that address advances in any of these topics.