This book is for graduate students and researchers who wish to understand theoretical mechanisms lying behind macroscopic properties of magnetic thin films. It provides a detailed description of basic theoretical methods and techniques of simulation to help readers in their research projects. The first part of the book contains 6 chapters. Chapters 1 to 5 focus on the fundamental theory of bulk magnetic materials. Chapter 6 is devoted to the presentation of the Monte Carlo simulation methods. Exercises and problems are provided at the end of each of these chapters for self-training. The second part contains 11 chapters devoted to the main topic of the book, namely "physics of magnetic thin films: theory and simulation." Written as a research paper, each chapter focuses on a subject and also presents the state-of-the-art literature on the subject and the motivation of the chapter. A detailed description of the techniques and the presentation of the results are then shown with discussion.