Low-dimensional systems have revolutionized semiconductor physics and had a tremendous impact on technology. Using simple physical explanations, with reference to examples from actual devices, this book introduces the general principles essential to low-dimensional semiconductors. The author presents a formalism that describes low-dimensional semiconductor systems, studying two key systems in detail: the two-dimensional electron gas, employed in field-effect transistors, and the quantum well, whose optical properties have multiple applications in lasers and other opto-electronic devices. The book will be invaluable to undergraduate and first-year graduate physics or electrical engineering students taking courses in low-dimensional systems or heterostructure device physics.