Endodontic emergencies are common in both general dental practices and specialist Endodontic practices. The aim of this review is to provide an overview of endodontic emergencies. Endodontic emergencies can be a result of many different conditions of the pulp, root canal and periradicular tissues. They may occur before endodontic treatment has been started, between appointments when treatment is being performed over multiple visits, or after endodontic treatment has been completed. In the latter situation, the emergency may be very soon after the treatment or it may occur many years later, in which case it is usually a new disease process as a result of the root canal system becoming infected. An emergency can be a stressful situation for both the patient and the dentist (or endodontist) as it is usually an unexpected event. It is incumbent on dental professionals to provide timely assistance to patients who have an emergency, and it is also important to allow sufficient time to manage the situation comprehensively. Management of endodontic emergencies should follow the principles of the 3D's – Diagnosis, Definitive dental treatment and Drugs – and in that sequence. An accurate diagnosis, the first "D", is essential so the appropriate treatment can be provided. Diagnosis requires a thorough understanding of the various conditions that can cause the emergency and this can be helped by having a comprehensive classification of the various conditions. The diagnosis should also direct the clinician to the appropriate definitive dental treatment, the second "D". Root canal treatment will not always be required as some cases can be managed conservatively. Other cases may require root canal re-treatment. The specific details of how the treatment is done can also vary, according to the diagnosis. The final "D" is Drugs – the use of drugs should also be dependent on the diagnosis and the dental treatment. Drugs should only be an adjunct following the treatment. The clinician must also differentiate between inflammation and infection in order to provide the appropriate treatment and to prescribe the appropriate medication for effective pain relief and resolution of other symptoms or signs such as swelling.