S G Tikhodeev and N A Gippius provide a brief introduction to nanoplasmonics, the optical properties of plasmon-polariton photonic crystals, and metamaterials. They also study the problem of determining the effective electromagnetic response of thin layers of metamaterials of an arbitrary symmetry, including gyrotropic ones. Nanoplasmonics is attractive, because plasmons allow concentrating electromagnetic energy in small volumes. Polaritonic crystals are artificial periodic media, in which optically active electronic resonances exist together with photonic resonances. Metamaterials are short-period metal-dielectric plasmonic crystals. One of the methods to obtain the effective dielectric and magnetic susceptibilities of a metamaterial is the parameterization of the experimentally measured or theoretically calculated coefficients of transmission and reflection of a finite-thickness layer of a metamaterial.