The book is designed for undergraduate students as well as first year graduate students. The book is divided into five chapters and two appendices. In the first chapter, we present an overview of modeling together with the classification of systems and models. The purpose is to give the student a big picture of the purpose of modeling, building steps for a model, the fundamental equations and the nature of the resulting model. In the second chapter, the student is introduced to the  practical aspects of modeling with the help of various examples that scan macroscopic models. In the third chapter, the student is exposed to various examples of microscopic models. In each example, the emphasis is put on the making of the right assumptions, the choice of the right control volume, the writing of the right balance equations and the analysis of the obtained model. The fourth chapter of this book is devoted to the presentation of the equations of change in various coordinates systems. Based on our experience, it is the building of microscopic models that presents the biggest challenge to the students. But once the equations of change are derived, they can be effective tools in the hand of the student to understand the physical meanings of the terms involved in the equation and to help him make the right simplifications for the model. The fifth chapter covers aspects of empirical modeling with emphasis on linear regression methods.