a b s t r a c t In this review, we show that the structure and behavior of single-walled nanotubes (SWNTs) are essentially polymeric; in fact, many have referred to SWNTs as ''the ultimate polymer''. The classification of SWNTS as polymers is explored by comparing the structure, properties, phase behavior, rheology, processing, and applications of SWNTs with those of rigid-rod polymers. Special attention is given to research efforts focusing on the use of SWNTs as molecular composites (also termed nanocomposites) with SWNTs as the filler and flexible polymer chains as the host. This perspective of ''SWNTs as poly-mers'' allows the methods, applications, and theoretical framework of polymer science to be appro-priated and applied to nanotubes.