This book emphisis on microflora responsible for failure of root canal treatment. Endodontic treatment is fairly predictable in nature with reported success rates up to 95%. However, along with these successful root canal treatments there comes inevitable percentage of non healed and endodontic failures .To understand the cause of failure of endodontic treatment it is important to completely understand the microbiology involved in the endodontic pathology. This will help us to modify the conventional treatment plans and effectively combat the microorganisms.