This book provides the required background to understand the fundamentals of industrial energy systems. It contains all modern approaches to assess, analyze and visualize the energy flows within the industrial energy supply systems including the entire supply chain. It provides a comprehensive understanding of the systems themselves as well as the tools and methodologies for studying and modelling the energy transfers. It addresses as well the economic analysis of energy efficiency measures with a special focus on consumption figures, incentives and legal requirements in Germany as an example of an industrialized nation in the energy transition. Sections cover the terms and methods to describe and optimize energy efficiency, the most recent technologies to save energy in the processes themselves as well as in facilities and premises and the background to understand industrial energy networks, like compressed air, steam and warm water systems. The audience includes a broad class of engineers and scientists dealing in their daily business with designing and optimizing industrial energy supply systems as well as undergraduate and graduate students of energy-related fields of study.