Gas sensors are essential for industry and for a wide range of applications. They are for examples applied in public safety, pollution monitoring, and various industrial processes. Among the different gas sensing technologies, semiconducting metal oxide-based gas sensors are the most popular because of their low price, high sensitivity, short response time, high stability and simple operation. In these gas sensors, because gas adsorption has a direct relationship with the surface area of the sensing material, a higher surface area will result in a higher sensing response. Therefore, along with simple synthesis methods, nanowires (NWs) have recently gained special attention for the realization of gas sensors. In this tutorial review, the synthesis of metal oxide NWs, the fabrication of gas sensors and their sensing mechanisms are discussed. Different gas sensors such as single NW, noble metal functionalized NWs, heterojunctions NWs, self-heating NWs, UV-activated NWs and core-shell NWs are presented. This tutorial review aims to provide a broad vision for the researchers and students working in this upcoming field.