This chapter of the book "Quantum Transport in Semiconductor Nanostructures" by C. W. J. Beenakker and H. van Houten provides an in-depth review of the transport properties of semiconductor nanostructures, focusing on two-dimensional electron gases (2DEGs) in silicon and gallium arsenide-aluminum gallium arsenide (GaAs-AlGaAs) heterostructures. The authors discuss the basic properties of these systems, including the density of states, Drude conductivity, Einstein relation, and Landauer formula. They also explore various transport regimes such as diffusive, quasi-ballistic, and ballistic transport, and the effects of magnetic fields on these regimes. The chapter covers classical size effects, weak localization, conductance fluctuations, the Aharonov-Bohm effect, electron-electron interactions, and quantum size effects. Additionally, it delves into the fabrication techniques for nanostructures, the measurement of transport properties, and the theoretical models used to understand the behavior of 2DEGs. The authors emphasize the importance of these studies in the development of innovative electronic devices and highlight the interdisciplinary nature of the field, involving physics, chemistry, and materials science.This chapter of the book "Quantum Transport in Semiconductor Nanostructures" by C. W. J. Beenakker and H. van Houten provides an in-depth review of the transport properties of semiconductor nanostructures, focusing on two-dimensional electron gases (2DEGs) in silicon and gallium arsenide-aluminum gallium arsenide (GaAs-AlGaAs) heterostructures. The authors discuss the basic properties of these systems, including the density of states, Drude conductivity, Einstein relation, and Landauer formula. They also explore various transport regimes such as diffusive, quasi-ballistic, and ballistic transport, and the effects of magnetic fields on these regimes. The chapter covers classical size effects, weak localization, conductance fluctuations, the Aharonov-Bohm effect, electron-electron interactions, and quantum size effects. Additionally, it delves into the fabrication techniques for nanostructures, the measurement of transport properties, and the theoretical models used to understand the behavior of 2DEGs. The authors emphasize the importance of these studies in the development of innovative electronic devices and highlight the interdisciplinary nature of the field, involving physics, chemistry, and materials science.