Adequate understanding and accurate characterization of normal and unusual root and canal morphology are essential requirements for successful root canal treatment. A new coding system for classifying root and canal morphology, accessory canals and anomalies has been introduced. In addition to technological advances related to experimental studies involving micro-computed tomography, the continuing clinical advances in magnification, illumination, imaging and intra-operative root canal treatment procedures have allowed clinicians to identify an increasingly wide range of anatomical variations in roots and canals in an attempt to achieve more predictable clinical outcomes. This review aims to provide a step-by-step explanation for the clinical application of the new coding system in dental practice, and to describe the anatomical variations in roots and canals for teeth scheduled for root canal treatment.