The carbon nanotubes are welcomed as the basis element for electronic and opto-electronic devices of nanometers size, the size of a few atoms. The question of crucial importance in the physics of utilization of nanotubes as nanowires, transistors, couplers etc. is the metal-nanotube interactions. In this thesis, we considered the problem of metal coverage of nanotubes and single atom-metal interactions, using the first-principles computational techniques. We had found that Ti, Fe and Ni bind strongly to the nanotube while Al, Cu and Au has weak binding. We propose that d orbital electrons of transition metal elements play important role in the strong interactions. We also observed that strong metalmetal interaction prevents uniform coverage of nanotube, however a stable ring and tube of aluminum atoms with well defined patterns can also form around the semiconducting SWNT’s and lead to metallization. We have obtained a criteria for the uniform coverage of nanotubes by metal atoms.