With the popularity of hardware security research, several edited monograms have been published, which aim at summarizing the research in a particular field. Typically, each book chapter is a recompilation of one or more research papers, and the focus is on summarizing the state-of-the-art research. Different from the edited monograms, the chapters in this book are not re-compilations of research papers. The book follows a pedagogical approach. Each chapter has been planned to emphasize the fundamental principles behind the logic locking algorithms and relate concepts to each other using a systematization of knowledge approach. Furthermore, the authors of this book have contributed to this field significantly through numerous fundamental papers.