Plasmonic nanoparticles (NPs) represent an outstanding class of nanomaterials that have the capability to localize light at the nanoscale by exploiting a phenomenon called localized plasmon resonance. The book is aimed at reviewing recent efforts devoted to utilize NPs in many research fields, such as photonics, optics, and plasmonics. In this framework, particular interest is devoted to active plasmonics, a quite broad concept that indicates those applications in which NPs play an active role, like realization of gain-assisted means, utilization of NPs embedded in liquid crystalline and flexible materials, and exploitation of renewable solar energy. The book puts together contributions from outstanding research groups in the field of plasmonic nanomaterials all over the world. It provides basic and advanced knowledge in the fields of plasmonics, photonics, and optics and covers research on plasmonic nanomaterials for applications ranging from plasmonics to photonics.