Root canal treatment is a dental procedure to clean and shape an infected tooth. During treatment several complications may occur among which Endodontic flare up becomes a nightmare for any dental practitioner. It is defined as an acute exacerbation of pain and/or swelling occurring after root canal treatment initiation or during continuation. It presents with an unscheduled patient visit and requires active treatment. Proper knowledge, identification and management of the same is crucial. Prevention focuses on proper diagnosis, strict aseptic techniques, controlled instrumentation, effective irrigation and the use of intracanal medicaments and educating patients about potential post-treatment discomfort and providing postoperative instructions are also essential. This book provides an evidence based guidance for the proper diagnosis and management of flare up cases.