As current silicon-based microelectronic devices and circuits are approaching their fundamental limits, the research field of nanoelectronics is emerging worldwide. Materials other than silicon and device principles other than complementary metal-oxide-semiconductor (CMOS) are being investigated. With this background, the present book focuses on nanoelectronic devices in InGaAs/InP based on ballistic and quantum effects. The main material studied was a modulation doped InGaAs/InP two-dimensional electron gas. The book covers mainly three types of devices and their twofold integration: in-plane gate transistors, three-terminal ballistic junctions and quantum dots. Novel device properties were studied in detail. The author hopes the results presented in this book to be a valuable contribution to the nanoelectronic research on InP-based semiconductors. The book should be interesting to semiconductor material scientists, device physicists and electronic engineers.