This dissertation describes the modification and functionalization of single-walled carbon nanotubes (SWCNTs). These SWCNTs were then investigated for their use in medical applications and for the storage of hydrogen. A technique was developed that leads to highly customized, individually suspended aqueous solutions of SWCNTs. These newly generated water-soluble SWCNTs were then functionalized further in water, thereby permitting the second functionalization addends to be chemically sensitive functional groups, for example drugs, that would not withstand the strongly acidic conditions of the first functionalization. The radical scavenging properties of nanovectors derived from SWCNTs were investigated and it was found that even the poorest SWCNT nanovector studied was nearly 40 times more effective at scavenging radicals than dendrite-fullerene DF-1, which has been shown to be a radioprotective to zebrafish via an antioxidant niechanism. This was used as the base to investigate using SWCNTs as protectors and mitigators of radiation exposure. SWCNTs were then explored for their use as drug delivery agents, in particular, the water insoluble chemotherapy drug, paclitaxel. SWCNTs showed promising in vivo and in vitro efficacy in the delivery of paclitaxel. Toxicity and biodistribution studies of the SWCNTs as drug delivery agents were performed in vivo using SWCNTs functionalized with radiolabeled indium. It was found that SWCNTs could be used for hydrogen storage by chemically crosslinking 3-dimensional frameworks of SWCNT fibers. These frameworks were shown to physisorb twice as much hydrogen, at low pressures, with respect to their surface areas, than typical macroporous carbon materials. This makes these SWCNT frameworks attractive materials for the development of a hydrogen vehicle fuel tank.