The effects of structure, purity, and alignment on the thermal conductivity of carbon nanotube-based films and fibers were studied experimentally to understand the heat transport phenomena occurring in the nanostructured materials. The thermal conductivity of the macroscopic films and fibers was determined by employing the parallel thermal conductance technique. The effects of different factors on the heat conduction properties were investigated to evaluate the roles of bulk density and cross-sectional area in the thermal conductivity of the nanostructured materials. The results indicated that macroscopic films and fibers produced from carbon nanotubes can conduct heat very efficiently, depending on a variety of factors. The structure, purity, and alignment play fundamentally important roles in determining the heat conduction properties of carbon nanotube-based films and fibers. Macroscopic films and fibers produced from single-walled carbon nanotubes typically possess high heat conduction properties. The non-carbonaceous impurities negatively affect the heat conduction properties because of the low degree of bundle contact. Carbon nanotube-based films and fibers give rise to a power-law dependence of thermal conductivity with respect to temperature. The specific thermal conductivity decreases with increasing bulk density. Low bulk density can compensate for the adverse effect of poor alignment on specific thermal conductivity. A maximum specific thermal conductivity is achieved at room temperature, but Umklapp scattering occurs. The specific thermal conductivity of carbon nanotube-based fibers is significantly higher than that of carbon nanotube-based films because of the increased degree of bundle alignment.