Boron-based thin film materials have numerous uses ranging from application as hard and refractory protective coatings to potential employment in wide-band gap semiconductor electronics. Of particular interest are the boron carbides, nitrides, oxides, and phosphides. These compounds exhibit a broad range of structural and bonding variations. The crystalline form of elemental boron is based on an arrangement of 12-atom boron icosahedra positioned at the vertices of a rhombohedral lattice. Related materials, such as B4C, and B12P, also possess structures closely related to this icosahedrally coordinated prototype. However, the structural coordination of the boron carbides and phosphides will vary with composition. For instance, BP possesses a tetrahedrally coordinated zinc-blende structure, and the carbon-rich boron carbides will form in a graphitic structure. Boron nitride has the added complication that for the same composition (BN) multiple bonding and polytypic variations are possible: both soft, graphitic sp2-rich (e.g., hexagonal and rhombohedral BN) and hard, diamond-like sp3-rich phases (e.g., cubic and wurtzitic BN) can be formed.