This volume is the proceedings for the 14th International Symposium on Aquatic Oligochaeta (ISAO), held in Hirosaki, Aomori Prefecture, Honshu, Japan, from 9 through 14 September 2018, organized by the Department of Natural Science, Faculty of Education, Hirosaki University, Hirosaki. The symposium was attended by 43 participants from 16 countries who presented 30 oral and 6 poster contributions. The scientific sessions were convened at the Iwaki Conference Hall in the 50th Anniversary Auditorium, Hirosaki University. In addition to the scientific sessions, there was a one-day excursion to visit a traditional playhouse Kouraku-Kan, lunch along the edge of Lake Towada – an oligotrophic caldera lake, and hiking along the lake’s outlet stream, Oirase-Keiryu, flowing through a cool temperate forest typical of northern Honshu. The symposium organizing committee consisted of Akifumi Ohtaka, Kimio Hirabayashi, Katsutoshi Ito, Mana Ito, Takaaki Torii, Naoya Kimura, Stuart R. Gelder, and Mark J. Wetzel, with invaluable support from students from Hirosaki University.