Potential energy curves and;spectroscopic constants for 45 low-lying electronic states of Nb-2, 18 electronic states of Nb-2(+), and 2 low-lying states of Nb-2(-) have been computed using the complete active space multiconfiguration self-consistent field followed by the multireference singles + doubles configuration interaction calculations that included up to 17 million configurations. The equilibrium distances (r(e)), vibrational frequencies (w(e)), and energy separations (T-e) are reported. We have also computed the properties of the two lowest electronic states of Nb-2(-). Possible assignments are suggested for the recently observed fragmentation spectra and three-photon fragmentation spectra of Nb-2(+) as well as the spectra of Nb-2. The dissociation energies. and ionization potentials of Nb-2 and Nb-2(+) as well as electron affinities of Nb-2 are computed. The nature of bonding is discussed using the wave function composition and Mulliken population analysis.