Successful endodontic therapy involves access cavity preparation, canal preparation, and three‐dimensional fluid sealed obturation of the canals. Canal preparation can be very challenging due to the complex morphology of the root canal system. The severity of root canal curvature is essential to select instrument and instrumentation technique. Severe canal curvatures of different degrees within the roots can lead to a variety of problems including ledge formation, separation of instruments, perforation, canal blockage or a teardrop transportation at the apex. The anatomical variations of complex root canal morphology often causes endodontic treatment failure, so it is necessary to have a thorough knowledge about tooth morphology. This paper reviews different methods use to determine the root canal curvature.