Materials are modeled by the ab-initio plane wave pseudopotential methods using density functional theory. In this book, we are seeking new ultrahard with enhanced elastic and mechanical properties, thermal stability as well as hardness which might be of advantage over known traditional materials - diamond and cubic boron nitride. Structural, elastic and electronic properties of the advanced metal nitrides M2N3 and their ternary phases were investigated using both the local density approximation (LDA) and the generalized gradient approximation (GGA). The relative stability of the ternary phases with respect to their constituent mixtures is computed. Results obtained are compared with the available experimental and theoretical data. To gain more information concerning the elastic properties of these hypothetical materials, we also computed the charge densities of the binary and ternary phases. From these calculations suggestions are made as to how the elastic properties vary from those of known hard materials.