We start with a brief look at the history of engineering and review how the field of industrial ecology emerged to help industries respond to growing concerns about pollution and resource scarcity. We then discuss the different notions of the concept of ecology as they relate to industrial ecology. After identifying the roots and basis of industrial ecology, we present the eco-industrial park idea, an industrial symbiosis concept that involves a cluster of companies who run their business while sharing resources and cooperating to minimize pollution and waste. As an engineering science, industrial ecology relies on quantitative methods. We discuss the role of the most important methods, including material flow analysis, life cycle assessment, and system dynamics. The chapter closes with a discussion on the sociometabolic approach.