Lismore is associated with Saint Moluag (Old Irish Mo-Luóc) (d. 592), who founded a monastery on the island. It was a major centre of Celtic Christianity, and the seat of the later medieval bishopric of Argyll or the Isles. To modern eyes it seems an isolated location for such a centre, but in an era when the fastest and most reliable transport was by water, Lismore was ideally situated. Of the cathedral only the choir survives, in greatly altered form, the nave and western tower having been reduced to their foundations. The building is in use as the parish church of Lismore.
Lismore is the home of the highland Clan MacLea, whose chief, Alastair Livingstone of Bachuil, Baron of the Bachuil is Coarb of Saint Moluag and, as such, the hereditary keeper of the saints crozier or pastoral staff (an early church relic known as the Bachull Mòr).
The Gaelic name, lios mòr, means "great garden" or "enclosure", reflecting either the fertility of a relatively low-lying island amidst mountainous surroundings, or the presence of a defined sacred area round the early monastery. In the 2001 census, the population was 146, over 45% of whom were over 60 years old, thus making it the Scottish island with the oldest population.