The major elements of a polycrystalline structure are grain boundaries. The energy of these grain boundaries is the source of the driving force of grain growth; their motion and interaction either mutually or with crystal dislocations constitute the mechanisms of recrystallization. The main properties of the boundaries, which are essential for the migration process, are the surface tension γ and mobility mb. As repeatedly mentioned, these properties are likely to diﬀer for diﬀerent grain boundaries. Furthermore, grain boundary surface tension and mobility can depend on the boundary orientation (inclination). The motion of a grain boundary segment is determined by the grain boundary shape in its closer vicinity.