During the last four decades voluminous literature has emerged on the metastable zone width, as determined by the maximum supercooling Delta T(max) using the conventional polythermal method, of various compounds in different solvents. The experimental data of maximum supercooling Delta T(max) for solute-solvent systems have traditionally been analyzed until now as a function of cooling rate R using Nyvlt's equation, proposed in 1968, which contains two empirical parameters (i.e. nucleation order m and nucleation constant k). However, the physical significance of these parameters in Nyvlt's equation has remained obscure until now. Since 2008 several papers have been devoted to the understanding of the effect of various experimental factors on the metastable zone width. The aim of this communication is to review these recent developments in the understanding of metastable zone width of solute-solvent systems. Finally, some general features of the dependence of Delta T(max)/T(0) on saturation temperature T(0) for different systems, the maximum supersaturation for isothermal crystallization and the effect of impurities are briefly discussed. (c) 2010 Elsevier B.V. All rights reserved.