From the mechanical point of view, polycrystalline materials have to be considered as a specific class of composites. They are composed of many grains, with grains size ranging from nm to cm scales. Grains are generally assembled in a random way, i.e. their size, shape, and lattice orientation do not depend on the size, shape, and orientation of the surrounding grains (figure 1). Therefore, the microstructure of polycrystals can hardly be described exactly. Most of the time, one can only access a statistical characterization of grain arrangement e.g. with the help of cross-correlation functions. In the Euler orientation space, microstructure description is generally limited to the distribution of crystal lattice orientations (Orientation Distribution Function, ODF, or crystallographic texture).