In this chapter “Step-back” and “Crown-down” technologies are well described as to how they differ from each other. Step-back technology is completed by using hand instrument like; files, reamers, broaches etc. and the apical 1/3rd portion of the root canal is prepared first, then secondly middle 1/3rd portion of the root canal is prepared, followed by last coronal 1/3rd preparation of the canal. But in crown-down technique of root canal preparation is done by rotary instruments (engine driven) and the order of step-back tec. Is reversed i.e. coronal 1/3rd is prepared first, then middle 1/3rd portion, and finally apical 1/3rd is prepared. Both these techniques have individual advantages and disadvantages. How and where to use which of these technologies or their combination, is distinctly described in this chapter. Recent development of root canal preparation under “Electron Microscope” is also described along with figures. A special feature of what is “Veterinary Dentistry” is also described. How and why full metallic crowns are fitted in pet animals (dogs, cats), filling, root canal treatment are also described using appropriate figures.