Abstract: The nucleation and growth of carbon nanotubes (CNTs) using chemical vapor deposition with a metalcarbon catalyst have been studied experimentally and theoretically. Results suggest that the nucleation and growth of multiwalled CNTs are not due to the metal alone, but that carbon nuclei (once formed) also contribute to radial and axial growth. Metal particles mainly promote the nucleation and growth of the innermost carbon shell(s), and catalyze the ordering of the carbon atoms to form graphene structures. The intrinsic difference between multiwalled CNT formation and singlewalled CNT formation seems to be associated with a selfcatalytic function of carbon nuclei.