Gas sensors based on SnO2 nanostructures have been extensively investigated in recent years. Many recent investigations have focused on synthesizing 0D, 1D, 2D and 3D SnO2 nanostructures with high sensing capacity. This work presents a review of the recent developments in pure, doped and metal oxide functionalized SnO2 nanostructured gas sensors, emphasizing the main SnO2 preparation methods and the working principle of SnO2 gas sensors. Most studies have shown that doping, coupled with a high surface area, can significantly improve SnO2 sensing properties. Sensing response, response/recovery times, and operating temperature can be modulated by the synergistic effect between these two factors. In general, fine nanoparticles, mesoporous materials, hollow and 3D nanostructures combined with additives such as Pt, Pd, Cu, Ni, Ag and Al have shown the best improvements in gas sensing.