What is a plasmon? Is it a particle like a photon or a wave? Plasmonics stands at the frontier of condensed matter physics, which is the world of electrons, optics and of photons. Plasmonics is one of the most active fields in nano-photonics. This book starts with the concepts of wave and the electromagnetic description of light when it interacts with metals and then dedicates every chapter thereafter to all aspects of plasmonics. In particular, the Surface Plasmon Polariton wave is explained in full detail as well as the Localized Surface Plasmon Resonance of metallic nanoparticles. The applications and the active research area opened by plasmonics are also briefly explained, such as advanced biosensing, subwavelength waveguiding, quantum plasmonics, nanoparticle-based cancer therapies, optical nano-antenna and high-efficiency photovoltaic cells.The book is adapted for graduate students and places a special emphasis in providing the complete explanation of the main fundamental concepts of plasmonics. Further, each of these concepts is illustrated with examples drawn from the most recent scientific literature. Each chapter ends with a set of exercises that will help the reader revise the concepts and go deeper into the world of plasmonics. More than 70 exercises are included.