Principles of Environmental Engineering is intended for a course in introductory environmental engineering for sophomore- or junior-level students. This text provides a background in fundamental science and engineering principles of environmental engineering for students who may or may not become environmental engineers. Principles places more emphasis on scientific principles, ethics, and safety, and focuses less on engineering design. The text exposes students to a broad range of environmental topicsincluding risk management, water quality and treatment, air pollution, hazardous waste, solid waste, and ionizing radiation as well as discussion of relevant regulations and practices.The book also uses mass and energy balance as a tool for understanding environmental processes and solving environmental engineering problems.