The introduction of ultrasonic technology in endodontics has revolutionized root canal procedures by enhancing precision, efficiency, and treatment outcomes. This book provides a detailed analysis of the science, research, and technological advancements behind ultrasonics, offering an evidence-based perspective on its growing role in endodontic therapy. The book starts by exploring the physics of ultrasonics, detailing how high-frequency acoustic energy is generated and applied in dentistry. It explains the working mechanisms of magnetostrictive and piezoelectric devices, discussing their advantages and limitations. The historical development of ultrasonics in dentistry is outlined, highlighting its gradual integration into endodontic procedures. One of the core areas covered is the impact of ultrasonics on root canal disinfection. The book presents scientific studies on passive ultrasonic irrigation (PUI), showing how ultrasonic activation of irrigants improves biofilm disruption, penetrates complex anatomy, and enhances debris removal. The role of ultrasonics in cleaning and shaping canals, removing intracanal obstructions, and refining access cavity design is also examined.