The current chapter offers a comprehensive and practical examination of hydrogen sensing technologies, driven by the characteristics of hydrogen, including its high diffusivity and low ignition energy, which render swift and dependable leak detection essential throughout the hydrogen value chain. The present chapter methodically investigates sensing needs that range from ppb-ppm trace detection to nearly 100% volume monitoring, all while considering challenging conditions such as temperature, pressure, humidity, and reactive environments. Moreover, the current chapter provides a thorough examination of the operating principles. This chapter covers materials, signal transduction mechanisms, and performance trade-offs related to various types of sensors, including thermal conductivity, electrochemical (amperometric and potentiometric), resistive metal oxide, work function-based (Schottky, MOSFET, and MOS capacitor), mechanical, optical, acoustic, catalytic, and the latest triboelectric sensors. The discussion examines several significant challenges, including cross-sensitivity, poisoning, hydrogen embrittlement, response-recovery kinetics, stability, power consumption, and miniaturization. Comparative insights reveal that the choice of sensors is fundamentally tied to specific applications, influenced by factors such as detection range, response speed, durability, and integration requirements. The chapter concludes that effective and scalable hydrogen deployment is fundamentally reliant on progress in materials engineering, sensor integration, and reliability to facilitate safe, real-time monitoring across production, storage, transport, and end use.