This paper presents results from molecular dynamics simulations of carbon nanotubes, showing that they have an unusually high thermal conductivity. The study uses equilibrium and non-equilibrium simulations with accurate carbon potentials to determine the thermal conductivity λ of carbon nanotubes and its dependence on temperature. The results suggest that an isolated (10,10) carbon nanotube has a thermal conductivity of approximately 6,600 W/m·K at room temperature, comparable to that of a hypothetical isolated graphene monolayer or diamond. This high value is attributed to the large phonon mean free paths in these systems. The study also compares the thermal conductivity of carbon nanotubes with that of graphite and graphene monolayers, finding that the thermal conductivity of graphite is significantly lower due to inter-layer coupling. The thermal conductivity of carbon nanotubes is found to decrease with increasing temperature, but remains high even at room temperature, exceeding that of nearly isotopically pure diamond. The results are supported by experimental data and show that the thermal conductivity of carbon nanotubes is very similar to that of a hypothetical isolated graphene monolayer. The study also highlights the importance of phonon mean free paths in determining thermal conductivity and suggests that the high thermal conductivity of carbon nanotubes is due to their unique structure and properties. The research was supported by the Office of Naval Research and DARPA.This paper presents results from molecular dynamics simulations of carbon nanotubes, showing that they have an unusually high thermal conductivity. The study uses equilibrium and non-equilibrium simulations with accurate carbon potentials to determine the thermal conductivity λ of carbon nanotubes and its dependence on temperature. The results suggest that an isolated (10,10) carbon nanotube has a thermal conductivity of approximately 6,600 W/m·K at room temperature, comparable to that of a hypothetical isolated graphene monolayer or diamond. This high value is attributed to the large phonon mean free paths in these systems. The study also compares the thermal conductivity of carbon nanotubes with that of graphite and graphene monolayers, finding that the thermal conductivity of graphite is significantly lower due to inter-layer coupling. The thermal conductivity of carbon nanotubes is found to decrease with increasing temperature, but remains high even at room temperature, exceeding that of nearly isotopically pure diamond. The results are supported by experimental data and show that the thermal conductivity of carbon nanotubes is very similar to that of a hypothetical isolated graphene monolayer. The study also highlights the importance of phonon mean free paths in determining thermal conductivity and suggests that the high thermal conductivity of carbon nanotubes is due to their unique structure and properties. The research was supported by the Office of Naval Research and DARPA.