In this article, we try to explain the basic concept of Gas Insulated Substation (GIS) and also the specifications of the GIS. We discussed the Electro-technical Commission (IEC) standards which are to be considered while selecting the switchgear. In this report, we come to know about various Advantages of GIS and the Hybrid system. We also discussed the applications of GIS and the cost required for GIS. In the end, we also give a comparison of air-insulated substation and gas-insulated substation.