Transition metal diborides are metallic ceramic materials with high electrical conductivities, refractory melting temperatures, and high hardness. Despite these attractive properties, the boride compounds have been overlooked in thin film science and technology relative to the carbides and nitrides. We employ the single-source, impurity-free precursors Hf(BH@sub 4@)@sub 4@, Zr(BH@sub 4@)@sub 4@ and Cr(B@sub 3@H@sub 8@)@sub 2@ to deposit stoichiometric thin films of HfB@sub 2@, ZrB@sub 2@, and CrB@sub 2@ by chemical vapor deposition. This talk highlights recent results on film microstructure, properties, and deposition mechanisms, which are analyzed using spectroscopic ellipsometry, line-of-sight mass spectroscopy, and trench coverage. Films grown at substrate temperatures of 200-300°C are diffraction amorphous and super-conformal in deep (20:1) trenches. The conformality is a consequence of site blocking which greatly lowers the precursor sticking coefficient. HfB@sub 2@ and ZrB@sub 2@ films are excellent diffusion barriers that prevent the mixing of Cu and Si during annealing up to 600°C. At growth temperatures @>=@ 500°C the films are crystalline and adopt a strong preferred orientation, including a normal texture on SiO@sub 2@ and pseudo-epitaxy on crystalline silicon (100) and (111) substrates. The latter may be good templates for heteroepitaxial growth of GaN, as previously reported. Amorphous HfB@sub 2@ can be crystallized by annealing at temperatures @>=@ 600°C. The post annealed films have an equiaxed, nanocrystalline structure with grain diameters of < 100 Å. Such films exhibit nanoindentation hardness as high as 40 GPa, exceeding the reported bulk value of 29 GPa. We create multilayered structures by periodically introducing a flux of atomic nitrogen during growth. This creates thin mixed phase layers that are softer; the ratio of hardness to modulus can be adjusted and the overall toughness increased.