This paper provides a comprehensive review of gas sensing technologies, focusing on their descriptions, evaluations, comparisons, and recent developments. The authors classify gas sensing methods into two main categories: those based on electrical property variations and those based on other property variations. Detailed discussions are given for sensing methods based on electrical variations, including metal oxide semiconductors, polymers, carbon nanotubes, and moisture-absorbing materials. Methods based on optical, calorimetric, acoustic, and gas-chromatographic variations are also presented. The paper highlights the importance of sensitivity and selectivity as key performance indicators and analyzes factors influencing these indicators. Several suggestions for future development are provided, emphasizing the need for improved sensitivity and selectivity in gas sensors. The paper concludes with a summary of the advantages, disadvantages, and application fields of different gas sensing methods.This paper provides a comprehensive review of gas sensing technologies, focusing on their descriptions, evaluations, comparisons, and recent developments. The authors classify gas sensing methods into two main categories: those based on electrical property variations and those based on other property variations. Detailed discussions are given for sensing methods based on electrical variations, including metal oxide semiconductors, polymers, carbon nanotubes, and moisture-absorbing materials. Methods based on optical, calorimetric, acoustic, and gas-chromatographic variations are also presented. The paper highlights the importance of sensitivity and selectivity as key performance indicators and analyzes factors influencing these indicators. Several suggestions for future development are provided, emphasizing the need for improved sensitivity and selectivity in gas sensors. The paper concludes with a summary of the advantages, disadvantages, and application fields of different gas sensing methods.