Solid-state nanostructures are constitutive and geometric nanononhomogeneities in semiconductor and dielectric mediums. Graphene, fullerenes and nanotubes, semiconductor structures with reduced dimensionality, such as quantum wells, wires and dots, and metallic nanoparticles, can be mentioned as examples. Despite their different physical natures, these objects share the common property of having extremely small dimensions in one or more directions. These dimensions are about one or two orders of magnitude bigger than the characteristic interatomic distance, and appear to be comparable to the electron’s de Broglie wavelength, thereby providing a discrete spectrum of energy states in one or several directions. Apart from that, the intrinsic spatial nonhomogeneity of nanostructures dictates nanoscale nonhomogeneity of electromagnetic fields in them. Complementary characters of these two key factors whose interplay drastically modifies the electronic and optical properties of nanostructures as compared to bulk mediums often escape the attention of researchers, especially if the research concerns electromagnetic waves in nanostructures beyond the optical range—the traditional scope of nanophotonics. The emergence of nanosized structures as key building blocks of nanoelectronic and nanophotonic devices extends the operational range of circuit components—e.g., interconnects, transmission lines, and antennas—to terahertz and far-infrared frequencies. Quantum mechanics come into play to a full extent in determining peculiar dispersion laws of components. Obviously, such an extension requires the development of new functional components and new physical models of their operation, as well as the radical modification of the basic principles of circuit theory, which conventionally relies on macroscopic electrodynamics. The potential of nanosized elements and nanostructured materials for electromagnetic fields manipulation and processing had motivated the recent invention of a new research discipline, nanoelectromagnetics, which conceptually is a fusion of classical electrodynamics with novel methods and approaches of condensed matter physics.