An extensive investigation of boranes, carboranes, and heteroboranes falling into the nido-8-vertex electron-count class has been carried out using ab initio methods. The results of this study indicate a nido six-membered open face geometry, ni-8[VI], is usually the preferred configuration over a nido five-membered open face geometry, ni-8[V]. In only two systems, B8H93- and OB7H72-, is a ni-8[V] geometry calculated to be of lowest energy. Attempts to test empirical carbon placement rules along with the skeletal bridge and endo-hydrogen location preferences were also evaluated. The results indicate the nido-8-vertex family is not ideally suited for the application of these empirical rules alone. This is probably due to the open face of these clusters not having homogeneous vertexes and/or not being "rigid". The ab initio/IGLO/NMR method was applied to the disputed B8H10. L and C4B4H8 systems. The known nido-B8H10. NEt8 was found to have a ni-8[VI] geometry with a fluxional bridge hydrogen. The calculations confirmed that the known alkylated derivatives of the nido-C4B4H8 carboranes have ni-8[VI] configurations in solution. In an investigation of B8H12, a previously unreported isomer of C-2 symmetry was found which high-level G2MP2 calculations indicate is only 1.6 kcal/mol higher in energy than the lowest energy C-2 symmetry isomer. This C-2 symmetry isomer is likely the higher energy intermediate in the degenerate interconversion of B8H12 into its mirror image. The transition state for the conversion of the C-s to the C-2 symmetry isomer has C-1 symmetry with a barrier of 2.1 kcal/mol at the MP2/6-31G* level of ab initio theory.