This book presents a comprehensive overview of research on environmentally friendly insulating gases, in response to the urgent calls for developing alternatives to SF6 due to the increasing awareness of the threat it poses as a greenhouse gas. It covers gas dielectrics, SF6 and its mixtures, and potential alternative gases, providing fundamental information on gas discharge and gas insulation and especially focusing on the development of new environmentally friendly insulating gases over the last decade. The book begins by describing the insulating and arcing characteristics of SF6, followed by an introduction to the gas dielectrics performance of SF6 gas mixtures with buffer gases. The latest findings on new environmentally friendly insulating gases are described in detail, and suggestions for practical application are also provided. Graduate students and teachers involved in high-voltage and insulation engineering can use the book as teaching material. Researchers working in plasma science, laser action and related applied physics fields can also benefit from the book's analytical approach and detailed data; engineers from the fields of electric power operation systems and electrical manufacturing will find it a valuable reference work for solving practical problems.