and precision, giving reliable tests on theoretical predictions. These basic concepts and appli­ cations to experiments have been recently reviewed by one of us (A. A. C. ) in "Modern Crystallography III. Crystal Growth" (Springer Series on Solid State Sciences, 1983). It has to be emphasized, however, that for practical applications we are still unable to quantitatively calculate many important parameters like kinetic coefficients from first principles. For mixed systems such as complex oxides, solutions and systems with chemi­ cal reactions, our degree of understanding is even lower. As a few examples for present achievements we note that experiments with vapour and molecular beam condensation of alkali halides confirmed the qualitatively predicted mechanisms of screw dislocations and two-dimensional nucleation for layer-growth.