The main interest around CNTs arises from their electrical roperties. Calculations verified by single-molecule experiments show that they are expected to be metallic or semiconducting depending on their structure, i.e. on their chiral vector. Armchair NTs show metallic properties while zig-zag and chiral NTs can be either metallic or semiconducting. Similarly shaped molecules consisting of only one element (carbon) may have very different electronic behaviour. At present, no synthetic method ensures a reliable control of the electrical properties of the NTs. The raw nanotube material thus consists of a mixture of metallic and semiconducting NTs (usually in ratio of 1:2). Separation of the metallic NTs from semiconductor ones is extremely difficult. CNTs possess highly valuable mechanical properties. Tensile strength 10 times larger than a steel wire of corresponding diameter, aspect ratio (length/diameter) is large and the density is low at 6 times smaller than that of steel. CNTs are extremely stable molecules and chemical functionalization of CNTs is difficult. CNTs possess two distinct region of different reactivity. One at the caps by the presence of five membered rings leads to a higher reactivity at thesepoints, comparable to that of fullerenes and the other on the walls which is more difficult to accomplish.