This book is about the current advancements in NiTi Rotary files that are being used extensively in the field endodontics. Various engine-driven NiTi endodontic files have been indispensable and efficient tools in cleaning and shaping of root canals for practitioners. In this book, we introduce the relative terms and conceptions of NiTi files, including crystal phase composition, the design of the cutting part, types, and newer advances. This book also helps in the analysis of the main improvement and evolution of different generations of engine-driven nickel-titanium instruments in the past 20 years in the geometric design, manufacturing surface treatment such as electropolishing, thermal treatment, and metallurgy. And the variety of motion modes of NiTi files to improve resistance to torsional failure are also discussed. Continuous advancements by the designers, provide a better balance between shaping efficiency and resistance to NiTi systems. In clinical practice, an appropriate system should be selected based on the anatomy of the root canal, instrument characteristics, and operators' experience.