Boron polyhedra can be described in terms of the deviation of their local vertex environments from the degree 5 vertices found in ideal icosahedra. Vertices of degrees other than 5 can be considered to be defective vertices. The most favorable structures for borane polyhedra are those in which the defective vertices are isolated as much as possible, similar to the Frank-Kasper polyhedra found in metal alloy structures. Using this criterion, the 9-and 10-vertex borane deltahedra are seen to be more favorable than the other nonicosahedral deltahedra in the boranes BnHn2- (6 less than or equal to n less than or equal to 12) in accord with experimental observations. Extension of such ideas to neutral boron hydrides of the type BnHn+4 accounts for the relatively high stability of B10H14, the formation of metal complexes of B6H10, and the stability of B18H22. In addition, the borane B12H16 is predicted to form stable transition-metal complexes.