In the present study the natural orbitals for chemical valence (NOCVs) combined with the energy decomposition scheme (ETS) were used to characterize bonding in various clusters of ammonia borane (borazane): dimer D, trimer TR, tetramer TE, and the crystal based models: nonamer N and tetrakaidecamer TD. ETS-NOCV results have shown that shortening of the B-N bond (by similar to 01 angstrom) in ammonia borane crystal (as compared to isolated borazane molecule) is related to the enhancement of donation (by 6.5 kcal/mol) and electrostatic (by 11.3 kcal/mol) contributions. This, in turn, is caused solely by the electrostatic dipole-dipole interaction between ammonia borane units; dihydrogen bonding, BH center dot center dot center dot HN, formed between borazane units exhibits no direct impact on B-N bond contraction. On the other hand, formation of dihydrogen bonding appeared to be very important in the total stabilization of single borazane unit, namely, ETS-based data indicated that it leads to significant electronic stabilization Delta E(orb) = -17.5 kcal/mol, which is only slightly less important than the electrostatic term, aEelstat = -19.4 kcal/mol. Thus, both factors contribute to relatively high melting point of the borazane crystal. Deformation density contributions (Delta rho(i)) obtained from NOCVs allowed to conclude that dihydrogen bonding is primarily based on outflow of electron density from B-H bonding orbitals to the empty sigma*(N-H) (charge transfer component). Equally important is the covalent contribution resulting from the shift of the electron density from hydrogen atoms of both NH and BH groups to the interatomic regions of NH center dot center dot center dot HB. Quantitatively, averaged electronic strength of dihydrogen bond per one BH center dot center dot center dot HN link varies from 1.95 kcal/mol (for the crystal structure model, N), 2.47 kcal/mol (for trimer TR), through 2.65 kcal/mol (for tetramer TE), up to 3.95 kcal/mol (for dimer D).