Research in optics and photonics, in parallel with the rapid development of nanoscience, has driven advancements within many fields of contemporary science and technology, allowing nano-optics to flourish as a research field. This authoritative text provides a comprehensive and accessible account of this important topic, beginning with the theoretical foundations of light localization and the propagation and focusing of optical fields, before progressing to more advanced topics such as near-field optics, surface plasmons in noble metals, metamaterials, and quantum emitters. Now in its third edition, the book has been substantially restructured, expanded, and developed to include additional problem sets and important topics such as super-resolution microscopy, random media, and coupled-mode theory. It remains an essential resource for graduate students and researchers working in photonics, optoelectronics, and nano-optics.