摘要： There are enormous functional materials which have been explored for gas sensing applications due to the fact that when a particular gas interacts with their surfaces, some alteration in their properties (optical, electrical, etc.) is observed. These functional materials are also termed as sensing ?lms, to be utilized as one of the essential components in a gas sensor. Other components include electrodes connected with sensing ?lm and data acquisition system coupled with it. During the past several decades, various metals, semiconductors, ceramics, and hybrid materials have been extensively explored for gas sensing applications. Selection of functional ?lm is dependent on the gas to be detected. A gas sensor should have some characteristics, viz., higher sensitivity, selectivity for target gas, least response and recovery time, higher reproducibility, and stability. Therefore, selection of appropriate sensing ?lm is highly required for a well-ef?cient gas sensor development. This article reviews the various kinds of sensing ?lms, their fundamental aspects along with the sensing mechanisms. Morphological changes in the materials and doping of other functional materials also affect the performance of a gas sensor. Hence, issues related to the ef?cient gas sensing are also covered in this article.