When a photon meets a nanostructure, many interesting phenomena occur. This book aims at developing the theories and the applications of photon interactions with nanostructures. The contributors were all participants in the well-known Japanese national research project, "Near-Field Nano-Optics", which ran from 1997 to 2000. The book covers a wide range of disciplines in nano-optics, including the theoretical development of imaging-contrast mechanisms as a result of photon and nanomatter interactions, and discussions on different near-field nanoprobes. Applications of nano-optics to sensing, imaging, analysis, and the fabrication of nanostructures, such as molecules and quantum devices, are also discussed, with a collection of experimental examples.