We have developed a novel strategy for cancer therapy based on absorption of near infrared light by nanoparticles, leading to rapid localized heating. The nanoparticles employed in these studies, gold nanoshells, have tunable optical properties, allowing design of particles with absorption or scattering essentially anywhere in the electromagnetic spectrum, including the near infrared region where transmission of light through tissue is optimal. Absorbing nanoshells are optimal for hyperthermia-based therapeutics, while scattering nanoshells are optimal for imaging applications. Gold nanoshells are also readily conjugated to antibodies, peptides or aptamers for targeting of either tumor cells or tumor vasculature. Complete tumor ablation and long term survival has been achieved in animal models. We have also demonstrated the feasibility of integrated imaging and therapy utilizing nanoshells designed to possess both absorbing and scattering characteristics.