A new approach is presented which has wide-ranging application for the modeling and understanding of both open multi-phase crystallization from the melt while the temperature is decreasing. and isothermal crystallization from Solution while solvent is evaporating. The results are widely applicable. Examples are given which relate to laboratory situations such as the liquid-phase epitaxial growth of complex III-V alloys and also to crystallization processes in oceans or sea water. (C) 2002 Elsevier Science B.V. All rights reserved.