This article provides a comprehensive review of humidity sensors, focusing on their principles, mechanisms, and fabrication technologies. The authors discuss various types of humidity sensors, including those based on organic and inorganic functional materials such as porous ceramics, polymers, ceramic/polymer composites, and electrolytes. The review highlights the transduction mechanisms and production technologies used in these sensors, and provides detailed performance characteristics, such as electrical and statistical data. The paper also addresses the challenges and advancements in sensor efficiency and conduction values, noting that thick film and thin film processes offer flexibility in material preparation and sensor structure design. The introduction covers the importance of humidity measurement in various applications, such as instrumentation, automated systems, agriculture, climatology, and GIS. The article is organized into sections that cover humidity basics, sensor classification, working principles, and specific types of sensors like impedance and capacitive transducers. The detailed analysis of ceramic humidity sensors, including their operation based on hydrogen permeation and water protonation, is a key focus. The review also discusses the development of humidity-sensitive materials, such as nanocomposites, and the synthesis and preparation of metal oxides for ceramic hygrometers and film-based humidity sensors.This article provides a comprehensive review of humidity sensors, focusing on their principles, mechanisms, and fabrication technologies. The authors discuss various types of humidity sensors, including those based on organic and inorganic functional materials such as porous ceramics, polymers, ceramic/polymer composites, and electrolytes. The review highlights the transduction mechanisms and production technologies used in these sensors, and provides detailed performance characteristics, such as electrical and statistical data. The paper also addresses the challenges and advancements in sensor efficiency and conduction values, noting that thick film and thin film processes offer flexibility in material preparation and sensor structure design. The introduction covers the importance of humidity measurement in various applications, such as instrumentation, automated systems, agriculture, climatology, and GIS. The article is organized into sections that cover humidity basics, sensor classification, working principles, and specific types of sensors like impedance and capacitive transducers. The detailed analysis of ceramic humidity sensors, including their operation based on hydrogen permeation and water protonation, is a key focus. The review also discusses the development of humidity-sensitive materials, such as nanocomposites, and the synthesis and preparation of metal oxides for ceramic hygrometers and film-based humidity sensors.