Abstract: Nano gas layer, a quasi-two-dimensional gassy absorbate located at the liquid-solid interface, still remains many open questions after relevant investigations for more than ten years. Based on the existing studies, the essential puzzles and significant achievements of the nano gas layers were summarized. The properties of nano gas layer, the relationship between the nano gas layer and nanobubbles, and their dynamic equilibrium were illustrated. More importantly, the current attention and controversies in this field, such as the gas phase authenticity, stability, structural order, and efficient preparation of the nano gas layer were introduced and discussed. Some suggestions to resolve these challenges were presented. This review reported the past development of research of nano gas layers as well as the prospect of their potential applications in some important interfacial reactions in the future.