Accurate working length (WL) determination is a crucial part of successful root canal therapy. Working length is the distance from the coronal reference plane to the apical constriction. The apical constriction, also referred to as cementodentinal junction, represents the transition between the pulpal and the periodontal tissues. It is widely accepted that canal preparation and filling should be terminated at that point. However, the location and form of the apical constriction are variable and not always detectable. Moreover, the available clinical methods used for WL measurements are also inaccurate. At present two methods are recommended in dental practice for determination of WL: radiographic technique, and by the means of electronic apex locators. Advantages and disadvantages of the two methods are discussed in this paper.