The Ancient Order of Hibernians (AOH) is an Irish Catholic fraternal organization. Members must be Catholic and either Irish born or of Irish descent. Its largest membership is now in the United States, where it was founded in New York City in 1836. Its name was adopted by groups of Irish immigrants in the United States, its purpose to act as guards to protect Catholic Churches from anti-Catholic forces in the mid 19th century, and to assist Irish Catholic immigrants, especially those who faced discrimination or harsh coal mining working conditions. Many members had a background with the Molly Maguires. It became an important focus of Irish-American political activity.

Background in Ireland:

The use of the name in Ireland goes back as far as 1565, when it was founded by an Irish chieftain, Rory O'Moore, to protect Roman Catholics against the religious persecution by the Lord Lieutenant of Ireland, Thomas Radclyffe, founded "The Defenders". The same source adds that: "It is impossible to give the exact date of the foundation of the order in Ireland." His part of Ireland was called Laois, and had been settled by the Catholic Queen Mary in the 1550s. This formative history was reported in the 1913 Catholic Encyclopedia but is not supported by any modern academic historians of the period. An anti-English and anti-Protestant sentiment prevailed in its ranks into the 20th century, by which time it had developed into a militant lay-Catholic mass movement similar to the Ribbon tradition.

At the end of the 19th century the AOH was reorganised in Ulster under its Grandmaster Joseph Devlin (later Member of Parliament) of Belfast. The AOH was closely associated with the Irish Parliamentary Party, its members mainly members of the party. The AOH was strongly opposed to secular idologies such as those of the Irish Republican Brotherhood who were most unhappy at the re-emergence of this old rival 'right-wing' nationalist society.

As a vehicle for Irish nationalism, the AOH greatly influenced the sectarian aspect of Irish politics in the early twentieth century. By 1914 had saturated the entire island, fuelled not so much by sectarianism as by its utility as a patronage, brokerage and recreational association. In Ulster and elsewhere it acted as an unruly but vigorous militant support organisation for Devlin, Dillon and Redmond against radicals and against William O'Brien: O'Brien regarded himself as having been driven from the party by Hibernian hooligans.

After the 1916 Easter Rising the AOH melted away outside Ulster, its members absorbed into Sinn Féin and the Irish Republican Army. In many areas the organisation provided by the AOH was the nearest thing to a paramilitary force. Many republican leaders in the 1916-1923 period, among them Sean MacDermott, J.J Walsh and Rory O'Connor, had been "Hibs" before the formation of the Irish Volunteers in 1913.

The AOH is also significant as a link between the new nationalist organisations and the century-old tradition of popular militant societies. More directly, it lingered on as a pro-Treaty support organisation. Some Hibernians fought in the Irish Brigade in the Spanish Civil War. The quasi-Fascist Blueshirts movement of the 1930s may, in fact, have owed as much to the Ribbon tradition which it so much resembled as it did to continental analogies.

Within Northern Ireland, the AOH remains a visible but somewhat marginal part of the Catholic community. It parades at Easter, Lady Day and a few other times a year.

United States:
The Order in the United States was founded in New York City May 4, 1836 at St. James Church located near the old Five Points neighborhood. Its existence and activities were concealed for some years. Its motto is "Friendship, Unity, and Christian Charity."
The Ladies Auxiliary was formed in 1894 in Omaha, Nebraska.

Most historians accept that for well over a decade in the late 19th century AOH acted as a "front" for the Molly Maguires. However alternative interpretations exist.
The Ancient Order of Hibernians coordinates the St. Patrick's Day Parade in New York City.