Composite fibers comprised of 5:95 wt ratio of ultra-short single walled carbon nanotubes (US-SWCNT):polyacrylonitrile (PAN) were spun using a dry-jet wet-spinning method followed by oxidative stabilization at 285 °C. The as-spun and stabilized composite fibers exhibited a 50 and 40 % increase, respectively, in modulus when compared to neat PAN. The vacuum pressure impregnation (VPI) method was employed to reinforce SWCNT fibers. SWCNT fibers were impregnated with polyamic acid (PAA) solution at 100 psi followed by thermal imidization to obtain fibers reinforced with polyimide (PI). The tensile strength was increased form 68 to 215 MPa for SWCNT fibers after VPI and imidization. Surfactant-wrapped chemically converted graphene (CCG) sheets obtained from the hydrazine reduction of GO were functionalized by treatment with aryl diazonium salts. The functionalized nanosheets disperse readily in polar aprotic solvents. A one-pot method has also been developed for reducing GO and simultaneously functionalizing it with alkyl and aryl groups. The alkyl functionalized reduced GO shows higher solubility in organic solvents when compared to GO. Graphene-filled PI composite films were prepared by solution blending of GO and PAA, casting the mixture and imidizing the films by heating up to 400 °C resulting in composite films that exhibit up to a ∼75 % increase in modulus and low moisture uptake. At 2 wt % loading GO, the composite films exhibit a conductivity of 1.25 × 10 -5 S/cm. The layer-by-layer (LbL) assembly technique was also employed in the fabrication of thin film composites of CCG and PI. The assembly was driven by the acid-base interaction between the aniline moieties on functionalized CCG and the carboxyl groups of the PAA. A simple fluid-phase processing method to obtain single to few layers of graphene without the aid of sonication has been developed. Graphene is spontaneously exfoliated from graphite and dissolved at isotropic concentrations as high as ∼1000 ppm in chlorosulfonic acid. The dissolution mechanism in superacids is protonation and electrostatic repulsion. The utility of this simple exfoliation process is further extended to diazonium functionalization of graphene allowing access to edge-functionalized graphenes with a minimal disruption of the graphitic network on the basal plane.