During nonsurgical endodontic retreatment, endodontic instruments are forced apically to remove the root canal filling material and regain canal patency. Undiscriminating burrowing down the canal in the apical direction may be fruitless and harmful. To avoid complications, the dentin overhanging the canal orifice must be removed and an unobstructed access established to the root filling material, so as to facilitate its removal. Reinstrumentation of the filled canal must take into consideration the nature of the filling material and the physical properties of endodontic instruments, as well as the dynamic aspects of canal preparation. This article discusses the mechanical considerations pertaining to root canal retreatment and outlines a step by step rationale approach to retreatment.