In Electron Gas: An Overview, the results of theoretical studies of the thermodynamic, kinetic, and high-frequency properties of the electron gas on the surface of a nanotube in a magnetic field in the presence of a longitudinal superlattice are presented. Following this, an interpretation of the basic transport characteristics of metals, superconductors in the normal state, and very strongly doped semiconductors with degenerate electron gas is presented. An application of the effective density of randomly moving electrons allows for an explanation of the conductivity of metals, and the electron transport characteristics such as the average diffusion coefficient, the average mobility, the mean free path, and the electron scattering mechanisms in a wide temperature range. Finally, the authors demonstrate high-performance InGaN-based light-emitting diodes with tunneling-junction-induced 2-D electron gas at an AlGaN/GaN heterostructure, which is inserted in the middle of the P++-GaN contact layer of a conventional LED structure.