A subtle change that leads to disastrous consequences-hardware Trojans undoubtedly pose one of the greatest security threats to the modern age. How to protect hardware against these malicious modifications? One potential solution hides within logic locking; a prominent hardware obfuscation technique. In this book, we take a step-by-step approach to understanding logic locking, from its fundamental mechanics, over the implementation in software, down to an in-depth analysis of security properties in the age of machine learning. This book can be used as a reference for beginners and experts alike who wish to dive into the world of logic locking, thereby having a holistic view of the entire infrastructure required to design, evaluate, and deploy modern locking policies.