The atomic and electronic structures of carbon nanotubes containing two of the major types of defect were determined using first-principles pseudopotential-based density functional theory calculations. Substitution with other atoms, and defects formed by the removal of C atoms from the otherwise perfect honeycomb graphene network were studied. It was found that doping with B or N atoms at various carbon sites of a carbon nanotube caused a simple shift in the Fermi energy, and a non-magnetic state. The energy cost associated with the formation of nanotube interconnects was evaluated by introducing a pair of heptagon and pentagons at the junction of two nanotubes, and it was shown how defects could lead to band structure control. A line defect for faulted carbon nanotubes was considered for carbon nanotubes which exhibited a stronger one-dimensional character of the charge densities and electronic structure, as compared with defect-free carbon nanotubes.Defect States in Carbon Nanotubes and Related Band Structure Engineering: a First-Principles Study. M.U.Kahaly: Journal of Applied Physics, 2009, 105[2], 024312