The metallic materials creep behaviour has been described and a complete model is presented. The basic constitutive equation, as well as the structure parameters, have been derived from a mathematical analysis that represents the dominant physical procedures and mechanisms. The model is very general because it is referred to all stages of creep and describes the creep behaviour of all metallic materials, including those strengthened by a dispersion of second-phase particles. A creep function has been derived from the constitutive equation describing all three stages of creep under constant loading. The function has the minimum possible number of fitting, parameters. The dependence of the fitting parameters on the loading conditions has been described using very simple mathematical relations. Applications and predictions have been carried out in a wide range of metallic materials. Good agreement has been shown by a comparison made also between the creep curves determined experimentally, and those obtained from creep function and determined fitting parameters.