The new emerging area of nanoscale optics is aimed at integrating photonics with nanotechnology and developing novel photonic devices for manipulating light on the nanoscale, including molecule sensing, biomedical imaging, and processing information with unparalleled operating speeds. This chapter provides an overview of research in nanoscale optics covering essential issues in the following areas: negative-index materials, local optical field enhancement in nanostructures, near-field optics, nanoplasmonics, and optical nanosensors. The size effect on the optical absorption spectra of metallic nanocrystals is probably best known for the noble metal nanoparticles. Optical properties of the noble metals, which directly reflect the size-dependent energy structure of the particles, are chosen as examples. Enhancement of the linear optical field of the optically excited medium over the metallic film is described by the following expression. The problems in using far-field optics to achieve nanometric spatial resolution are formidable.