The essential role of microorganisms in the initiation and perpetuation of pulp and periapical pathosis has been well documented. The major objective in endodontic therapy is to disinfect the entire root canal system. Considering the complex anatomy of the root canal system, complete elimination of bacteria by cleaning the root canal with instrumentation alone is unlikely. Therefore, an appropriate antimicrobial irrigant is needed to decrease the microbial load, especially in necrotic and retreatment cases. Another important issue in endodontics is the smear layer. Although there is no general consensus on removal of the smear layer, it seems that removing it enhances the sealing ability of the root canal filling. MTAD is an endodontic irrigant with both antibacterial and smear layer removal abilities. The aim of this paper is to review these different aspects of MTAD.