The study of hagiographies has generally been focused on the more prominent saints of late antiquity and the Middle Ages who inspired significant and long-lasting veneration. However, this has caused many less-well-known saints to be pushed aside and forgotten.This book is a study into one such saint, Irenaeus, a martyr who was killed in 304 CE in Sirmium, Pannonia. His short-lived cult, his feast day, and the account of his martyrdom (which had been translated into Latin, Greek, Old Slavonic, Georgian, and Armenian) had all been forgotten during the Middle Ages. This book examines Irenaeus of Sirmium’s life, cult, sainthood, and eventual disappearance from the memory of medieval Christendom, in the context of a wider study on the memory of those less-well-known saints who, like Irenaeus, became neglected and eventually forgotten.Irenaeus of Sirmium and His Story in the Medieval East and West will be of interest to scholars and students alike interested in hagiography, medieval literature and history, as well as all those interested in the religious history of Byzantium, medieval Europe, and the Slavic world.