Double-walled carbon nanotubes are coaxial nanostructures composed of exactly two single-walled carbon nanotubes, one nested in another. This double-wall structure makes DWNTs the simplest system for studying the effects of inter-wall coupling on the physical properties of carbon nanotubes (CNTs). Compared to single-walled carbon nanotubes (SWNTs), DWNTs have higher mechanical strength and thermal stability and they also possess interesting electronic and optical properties.

DWNTS are used in applications such as: Field effect transistors, mass sensors, ultra-fast optical switches, nanomotor/nanobearing, capacitors, solar cells etc. DWNTS exhibit higher stability, which can be a substantial help in high-current and high-field experiments as, e.g., in field emission applications.

Double wall carbon nanotubes have been considered as potential candidate for ultra-high frequency oscillator. The DWCNTs are separated into four categories wherein the inner–outer nanotubes are metal–metal, metal–semiconductor, semiconductor–metal and semiconductor– semiconductor single-wall nanotubes.

The band structure of a DWCNT depends on the combination of the configurations of the inner and outer tubes and their stability depends only on their inter layer spacing. The presence of a shielding outer wall is especially appealing for chemical and biological sensors, as it allows for chemical modification of the outer shell while maintaining the electrical properties of the inner pristine core.