A plethora of new technology in endodontics has been available over the last 30 years, yet the outcome measures of success have changed very little. The clinician must be aware that the goal of non-surgical root canal treatment is fundamentally a biological one and the instrumentation of the canal serves to facilitate this approach. Adequate irrigation, disinfection, antimicrobial medication and subsequent obturation and final restoration all play key roles in preventing reinfection. Key factors that can have a negative impact on outcome are discussed.