We have developed two novel synthetic methods for carbon nano-tubes, namely the high-temperature pulsed arc discharge (HTPAD) method and the hot filament-assisted chemical vapour deposition (HFCVD) method. These methods can provide selective syntheses of single-, double- and multi-wall carbon nanotubes. HTPAD can produce high-quality double-wall carbon nanotubes (DWNTs) with Y/Ni alloy catalysts at 1250 °C. Their catalytic roles on the synthesis of DWNTs are investigated by controlling the compositions of Y and Ni, resulting in the optimum conditions of 2.5 and 4.2 at%, respectively. No DWNTs, but only SWNTs, can be produced without Y, which shows the importance of Y in the production of DWNTs. HFCVD, on the other hand, using ethanol as a carbon source, can produce high-purity SWNTs with high efficiency. The production rate of SWNT synthesis has been increased by the hot filament-induced pyrolysis of carbon sources, which promises an easy scale-up of the production of SWNTs at low cost.