We have simulated the melting behaviour of metal and non-metal clusters for the size of 12 less than or equal to n less than or equal to 34, where n is the number of atoms. We find that the non-monotonic variation of melting temperature with size, the dependence of melting, boiling, and sublimation temperatures on the potentials, the existence of a surface-melted phase, and the absence of a premelting peak in heat capacity curves can be explained by the relative stability of the internal atoms to the surface atoms in the clusters. (C) 2001 Elsevier Science B.V. All rights reserved.