The introductory chapter, “Introduction to Next-Generation High-Speed Electronics and Optoelectronics (Vol. 1),” situates the field at the confluence of terahertz (THz), infrared (IR), and millimeter-wave (mm-wave) technologies and explains why this spectral span—bridging electronics and photonics—demands fresh thinking from materials to systems. It outlines how wide-bandgap (WBG) semiconductors (notably GaN and SiC), advanced heterostructures, and high-electron-mobility devices enable high-power, high-frequency operation, while integrated photonics consolidates optical and electronic functions on common platforms for compact, energy-aware front ends. The chapter then organizes the design space around cross-cutting challenges—thermal management, noise control, and scaling—showing how circuit topologies and fabrication advances preserve signal integrity as frequencies rise. Two emerging levers, machine learning and engineered media, are highlighted for accelerating device/circuit codesign and achieving tailored wave interactions: neural models shorten design cycles and support adaptive operation, while metamaterials and quantum dots open pathways to fast detection, modulation, and novel passive components. Finally, the chapter connects these technical threads to applications across 6G-class communications, high-resolution medical and security imaging, and autonomous sensing, emphasizing the need for materials–device–circuit–system co-optimization to meet stringent performance targets. Collectively, this framework provides the conceptual scaffolding for the volume, guiding readers from fundamentals to fabrication-aware, application-ready solutions.