Not Available Single wall carbon nanotube - polymer composites will be synthesized and investigated for EMI shielding applications. Bundles of nanotubes will be prepared by an arc discharge process and dispersed in several polymer hosts as a physical mixture. Composites made from as-grown and chemically purified nanotubes will be investigated as a function of the vol.% loading, as will composites formed by laminating large area sheets of nanotube paper between polymer sheets. The effects of enhanced nanotube conductivity (chemical doping) and ferromagnetic nanoparticle additives will also be addressed. Stripline cavities operating in the 0.075 - 6 GHz range will be used to measure the complex permittivity and permeability of the composites. When applicable, the results will be modeled using an effective medium theory for composites built from dielectric hosts containing high aspect ratio conducting rods.