This chapter contains the theoretical foundation of the book by introducing the topic area of business processes and modeling and the most important concept underlying modeling of business processes. After introducing high-level aspects of business process management, business process modeling is grounded in general model theory and the chapter describes the philosophy underlying the approach to the quality of models by providing an overview of the most important goals of modeling. We also exemplify this by introducing some of the cases and modeling notations used later in the book, including an introduction to BPMN, variants of which are used in several of the cases presented.