This magisterial graduate and advanced undergraduate book is highly recommended for its unique features. All the steps of the derivations are included, and the key equations are boxed. Various approaches to the theory are derived and critically compared, stressing their validity and limitations . The text isaugmented by color figures, six comprehensive mathematical appendices, problem sets for each chapter, and access to the NANOPT toolbox of MATLAB files. (Barry R. Masters, Optics & Photonics News, osa-opn.org, June 17, 2021)