The first part of this chapter is concerning cases of exploratory surgery. The section about alleviation of symptoms of apical periodontitis focuses on drainage. Indications for endodontic surgery in cases of ongoing root canal treatment are discussed. A method for retrograde root canal treatment in case of difficult orthograde access is presented. The discussion about root-filled teeth without unsatisfactory healing results occupies lion’s share of this chapter. Special attention is given to the controversies of “success” and “failure” in endodontics. Factors that generally point to a surgical approach to endodontic retreatment are examined. The meaning of informed consent is in particular focus. This chapter ends up with an examination of the medical considerations, which is the basis for the risk assessment of the individual patient compulsory before any endodontic surgery.