This document discusses gas insulated substations (GIS), which use sulfur hexafluoride (SF6) gas as an insulating medium. GIS offer advantages over conventional air insulated substations, as they are more compact and reliable. The key components of a GIS include busbars, circuit breakers, disconnectors, and current/voltage transformers housed in metal-enclosed modules filled with SF6 gas. While GIS have higher initial costs than air substations, they require less space and have lower maintenance needs. However, SF6 is a greenhouse gas so future GIS may use alternative insulating gases or SF6 mixtures to reduce environmental impact.