This book presents a comprehensive overview of RTL (Register Transfer Level) debugging, addressing both foundational concepts and emerging technologies. It begins by examining the key issues faced in RTL design, such as timing violations, limited signal observability, and complex verification environments. It then outlines the basic principles of RTL debugging, including simulation techniques, waveform inspection, and the use of assertions and testbenches. Traditional debugging methods are discussed in depth, highlighting techniques like print-style debugging, coverage analysis, and assertion-based verification, along with their respective advantages and limitations. The book concludes with an exploration of leading-edge approaches involving Large Language Models (LLMs), showcasing how AI can support RTL debugging by assisting in code comprehension, anomaly detection, and bug localization.