The classical electromagnetism described by the Maxwell equations constitutes a fundamental law in contemporary physics. With the advent of sophisticated new materials, the principles are still active in various applied areas in todays advanced communication technologies. Referring to modern materials, this book is written with concise introductory arguments for the physics of electromagnetism, covering basic topics including the nature of space-time-dependent radiations in modern applications. However, noted that the classical concept fails generally at optical frequencies, the limit is a significant obstacle for further technical developments. Following basic discussions of electromagnetism in a modernized approach, this book provides readers with an overview of current problems in high-frequency physics. Although written primarily for students of physics and engineering at undergraduate levels, this book should serve as a useful reference for graduate students and researchers as well. The subject matter in this book is all fundamental, although given examples may appear a little too specific.