Abstract: Prior to root canal treatment at least one undistorted radiograph is required to assess canal morphology. A correct working length with the help of Radiograph or Electronic Apex Locator is one of the critical factors for the success of Endodontic Treatment. Short measurements may leave parts of the Root Canal un-instrumented. On the other hand, over instrumentation with enlargement of the apical constriction may result in damage to peri radicular tissues. Therefore correct working length has a role in treatment success. Compared to Radiograph, Electronic Apex Locators reduces the number of radiographs and assists where radiograph method is difficult to access. This review of literature focusses on the insight into electronic apex locator. Search engines used are, PubMed and Google Scholar.