In the 19th century various tricolour flags and ribbons came to be symbolic of Irish nationalism. Many of them included the colours green (for the Roman Catholics), orange (for the Protestants), and white (for peace between them). The first known vertical tricolour flag of orange-white-green dated from March 1848, but it was not until 1917 that it gained widespread popularity. The tricolour in its modern form (green-white-orange) was recognized by the constitution on December 29, 1937, and was not altered when the Republic of Ireland ended its participation in the British Commonwealth on April 18, 1949. It is often incorrectly asserted that the third stripe is yellow or gold rather than orange.

A number of official and unofficial flags over the centuries have been flown in Ireland. One of the earliest, in use in the late 15th century, was blue with a gold harp; today it is the presidential standard of Ireland. In the 17th century the Cross of St. Patrick—later incorporated into the British Union Jack—was widely employed. White with a red diagonal cross, it was associated both with the family arms of the Fitzgeralds and with the Spanish Cross of Burgundy (a red diagonal cross used in Spain since the 8th century). In the mid-17th century a green flag with a golden harp, attributed to the province of Leinster, came to be recognized as the flag of Ireland even though the island was under English rule. This was one of the flags flown during the 1916 Easter Rising, which led to the establishment six years later of the Irish Free State.