The Annals of Ulster are annals of medieval Ireland. The entries span the years from 431 AD to 1540 AD. The entries up to 1489 AD were compiled in the late 15th century by the scribe Ruaidhrí Ó Luinín, under his patron Cathal Óg Mac Maghnusa, on the island of Senadh-Mic-Maghnusa, also known as Senad or Ballymacmanus Island, near Lisbellaw, on Lough Erne in the kingdom of Fir Manach (Fermanagh). Later entries were added by others.

Lough Erne is the name of two connected lakes in County Fermanagh, Northern Ireland. It is the second-biggest lake system in Northern Ireland and Ulster, and the fourth biggest in Ireland. The lakes are widened sections of the River Erne, which flows north and then curves west into the Atlantic. The smaller southern lake is called the Upper Lough as it is higher up the river. The bigger northern lake is called the Lower Lough or Broad Lough. The town of Enniskillen lies on the short stretch of river between the lakes. The lake has more than 150 islands, along with many coves and inlets. The River Erne is 80 miles (129 km) long and drains an area of about 1,680 square miles (4,350 km2).