Ab initio quantum-mechanical studies employing basis sets approaching the quality of triple-zeta plus double-polarization for A1 and N and single-polarization for H are reported for bis(ammonia)alane [A1H(3)(NH3)(2)] = bAA and its dissociation products. The self-consistent-field method was employed for all basis sets; the single- and double-excitation configuration-interaction and comparable coupled-cluster methods were utilized with the double-zeta plus polarization functions basis set. The dissociation energies are predicted to be 8 kcal/mol for the first ammonia and 31 kcal/mol for the second, after correcting for zero-point vibrational energy. The results indicate small structural differences between isolated ammonia and the ammonia moieties in bAA. However, the A1-N bond lengths are 2.20 Angstrom, compared to 2.08 Angstrom in (ammonia)alane. There appears to be a problem with the experimental electron diffraction structure for bAA. This work corrects earlier experimental assignments of the A1-N stretching vibrational modes. Harmonic vibrational frequencies, infrared intensities, and atomic charges are reported. These results indicate that very little charge transfer occurs compared to that for normal dative bonds.