The carbon nanotube (CNT) is a representative nano-material discovered in 1991 at NEC. With its unique structure, high strength, high electric conductivity and high thermal conductivity, CNT is expected to be applied widely together with its variant the carbon nanohorn (CNH) in electronic devices such as transistors and fuel cells as well as in the environmental and biotechnological fields. This paper introduces the characteristics and features of CNT and CNH and describes some of their application fields.