This book describes the essential characteristics of graphene, graphene oxide, reduced graphene oxide, and its nanocomposite and their applications in water and wastewater treatment and other environmental issues. The book introduces each topic in detail, discusses the basic principles, and analyzes and summarizes recent developments in the field. Various topics covered in this book include role of graphene as a potential material in photocatalytic organic pollutant degradation, water splitting applications, capacitive de-ionization techniques, air purification, gas adsorption, and decontamination of pathogenic microorganisms. Given the contents, the book is useful for students, researchers, and professionals working in the area environmental science and materials, especially graphene oxide, graphene, and graphene nanocomposite.