Surface plasmon photonics (“plasmonics”) is an expanding field at the frontiers of optical science and engineering, concerned with the interaction of light with metallic structures. Surface plasmons are coupled electromagnetic/charge-density waves propagating along metal-dielectric interfaces or localized at metal nanostructures. Light suitable for exciting surface plasmons is typically within or near the visible but may extend into the infrared and ultraviolet regions. Metallic structures that support surface plasmons are highly varied, including planar arrangements of metal films, stripes or grooves, metal gratings, and metal nanoparticles such as islands, spheres, rods, or antenna-inspired structures. Surface plasmons can be localized at subwavelength scales, and, for example, are involved in optical transmission through one or several subwavelength holes in a metal film, in what is now referred to as “extraordinary optical transmission.” Surface plasmons are intimately involved in the response of “metamaterials” and “metasurfaces” constructed from deep subwavelength metallic features, producing esoteric macroscopic properties such as a negative refractive index, or a permittivity/permeability near zero.