Nitride formation is fairly common among the transition elements and the actinides. Diffusion data exist for mononitrides of Ti, Zr, Nb, Al, Th, U and (U, Pu), as well as for Si3N4, Cr2N, Fe4N, Li3N and KN3. As with the monocarbides of transition metals and actinides, large single-phased regions of substoichiometric mononitrides exist. Information on sample preparation and measurement methods are tabulated in this chapter. Semilogarithmic plots of diffusion in nitrides are presented as well.