Deformation mechanism maps are a very useful tool for displaying deformation mechanisms as a function of the three fundamental parameters of high temperature flow: the applied stress, the testing temperature and the grain size of the material. These maps are used extensively in the field of high temperature creep but there has been very little use with ultrafine-grained (UFG) metals. This article reviews the principles of deformation mechanism maps, presents examples of maps for some representative metals processed by equal-channel angular pressing or high-pressure torsion and then describes a simple procedure for constructing maps for UFG materials.