|In-situ TEM under gaseous environment is a powerful tool for various nanomaterial-based technologies, such as efficient energy conversion, transportation, food production and environmental protection. The practical information obtained from in-situ TEM observations of gas–solid interactions promises new insights into the growth, properties, and functionality of nanomaterials such as catalysts, fuel cells and biological molecules. Either windowed gas cell or differential pumping approach is used to realize in-situ TEM observations under gaseous environment. The windowed gas cell approach has various advantages over the latter, including a much thinner gas path length, a better resolution, a higher pressure limit, much more rapid thermal response, more rapid stabilization of specimen drift, and a much lower cost, etc. However, a comprehensive review of windowed gas cells for in-situ TEM observations is missing to summarize the achievements to date in this field. This article serves to fill this gap.