Phase transitions denote transformations of the substance in one phase to another phase. The description of phase transitions is realized essentially within two schemes: a sharp interface across which the constitutive properties suffer a sudden change or a diffuse space region where the pertinent fields vary continuously. First, the jump conditions are derived for the interface among two phases. Next details are determined for the liquid-vapour transition, thus finding the continuity of the Gibbs free energy at the interface and Clapeyron’s equation. The brine channels formation is also developed and the solidification-melting of binary alloys is described. Phase transitions in shape-memory alloys are modelled.