Ireland is the neighbouring island to the west of the Isle of Man, separated by the Irish Sea. The relationship between the two islands has been close throughout history, with extensive cultural, linguistic, and trading connections. Manx smuggling severely affected Irish revenues during the eighteenth century, contributing to Ireland's support for the Revestment, and the annuity granted to the Duke of Atholl after 1765 was charged upon the Irish revenue.

Irish revenues paid for the Island long before that. When Reginald, King of Mann, did homage to King John in 1205, the charter provided that he should receive a knight's fee of two tuns of wine and a hundred and twenty quarters of corn yearly out of Ireland.

The two islands' governors overlapped. Sir John Stanley the first, the first Stanley Lord of Man, was appointed Governor or Lieutenant of Ireland by Richard II about 1379, held the office until 1389, and was made Lord Justice of Ireland in 1390. A band of Irish under Richard de Mandeville ravaged the Island in 1316.

The Irish saints made the Island Christian. St Patrick converted it about 447 and left Germanus as its bishop. St Maughold came ashore from Ireland in a leather boat with irons on him and became bishop by the suffrage of the Manx nation. St Bridget came over to take the veil from Maughold, and the Nunnery at Douglas was ascribed to her.

Trade policy set the two against each other. Lord North spoke against admitting the importation of cotton into Ireland, and Ireland's obtaining the privilege of exporting cotton yarn in 1778 is one of the circumstances Manx economic historians cite when they come to the Island's own short-lived cotton trade.