The root canal filling concludes the classical triad in endodontic treatment: biomechanical instrumentation, disinfection and obturation. The purpose of the root canal filling is to prevent penetration of bacteria into the root canal and to prevent access of nutrients and growth of residual bacteria. The function of the root canal filling is to seal and obturate the root canal and kill remaining microbes. This is achieved most often with the use of a core material and a sealer. The core material acts as a piston to push the sealer out to fill the root canal system. In addition to achieve intimate contact with dentin, the sealer has contact with periapical soft tissue. Therefore the sealers have to fulfill both technical and biological requirements. The endodontic treatment ends with a coronal seal to prevent coronal leakage of bacteria. A technically well performed root canal filling, acceptable filling length and homogenous root filling, evaluated radiographically, with an adequate coronal restoration, is a reliable predictor for a successful outcome.