There are excellent methods for modelling physical and elastic properties, for example, those based on ab initio atomistic procedures. For mechanical properties that are controlled by the motion of the dislocations, such methods have not been available in the past. One has been forced to resort to fitting the experimental data with empirical methods by involving a number of adjustable parameters. However, in recent years, methods based on physical principles have been developed for a number of mechanical properties. These methods can predict properties accurately without the use of fitting parameters. A review of such methods will be given, for example, for the modelling of creep deformation in metallic materials. It will be demonstrated that some properties can be described over a wide range of temperatures and strain rates. The advantage of these new methods is that they can be used for prediction, identification of mechanisms and extrapolation of results for new conditions.