Microorganisms play an unequivocal role in infecting root canal system. Endodontic infections occur and progress when the root canal system gets exposed to the oral environment by one reason or the other and simultaneously when there is fall in the body's immune response.Endodontic therapy's substantial purpose is to create a biologically appropriate environment within the root canal system that is conducive for the healing and maintenance of periradicular tissue health. Bacteria are one of the main factors causing disorders in the pulpal tissues, as they invade the endodontic space through variety of routes, including carious lesions, traumatic pulp exposure, using blood stream or by adjacent tissues. Bacteria found in the pathogenesis of endodontic diseases vary from facultative anaerobes to aerobes to the most resilient species able to survive adverse conditions in the surrounding environment. By using irrigation, mechanical action, and the antibacterial properties of the irrigating solutions, bacteria eradication and postendodontic treatment success are assured.