This book systematically introduces the common solid, liquid, and gas insulating materials used in electrical engineering, providing a comprehensive analysis of their fundamental properties, such as insulating characteristics, mechanical properties, dielectric properties, and thermal properties. Additionally, it discusses innovative sustainable developments in insulating materials, including self-healing, degradable, and recyclable options. The book focuses on the development trends and directions of electrical insulating materials in the context of the green transition, delving deeply into the current challenges and contradictions in research. Furthermore, it introduces readers to future developments and innovations, aiming to provide low-carbon, eco-friendly, and sustainable insulating solutions for the power industry and drive innovation and advancement in the field of electrical materials. By systematically reviewing both foundational research and cutting-edge applications of low-carbon, eco-friendly, and sustainable insulating materials, this book facilitates a deeper understanding of new milestones and sustainable developments for researchers and professionals across various disciplines.