Ectopic eruption of the maxillary first permanent molar is a developmental disturbance of path of eruption resulting in distal root resorption of the second primary molar. Irreversible ectopic eruption causes mesial tipping and rotation of the permanent molar, and space deficiency of the permanent second premolar. The purposes of this article are (1) to review the literature on ectopic eruption of the maxillary first permanent molar, and (2) to discuss the prevalence, etiology and classification or ectipic eruption of the maxillary first permanent molar, and (3) to introduce several treatment techniques.