St. Nicholas' Collegiate Church, Medieval parish church in Galway, Ireland

St. Nicholas' Collegiate Church is a hall church of three aisles of near-equal height under parallel roof ridges, a type common in the Netherlands, Flanders and southern England. Inside, some bays have wooden barrel vaults while others are open to the roof timbers. It is the largest medieval parish church in Ireland still in continuous use.

Founded in 1320 and dedicated to Saint Nicholas, patron of seafarers, the church was raised to collegiate status by letters of Donatus Ó Muireadhaigh, Archbishop of Tuam, on 28 September 1484, confirmed by Pope Innocent VIII's bull Super Dominicum Gregem on 8 September 1485. A College of Vicars headed by a warden, a title unique in Irish ecclesiastical history, governed the city's parishes. The Reformation created rival Anglican and underground Catholic wardenships, both ended in the early 19th century.

The church is used today by Church of Ireland, Romanian and Russian Orthodox, and Malankara Mar Thoma Syrian congregations. Each year on the Sunday before Christmas, the Civic Carol Service of Nine Lessons and Carols is attended by the Mayor and City Council in ceremonial robes with the Great Mace and Civic Sword.

St. Nicholas' stands on Lombard Street in the centre of Galway, a short walk from Shop Street and the Spanish Arch. The building is entered through its main door on the south side; the three parallel aisles make it easy to walk around the nave. Services are held regularly, including worship by Romanian and Russian Orthodox and Malankara Mar Thoma Syrian congregations, so check times before visiting.

The Leabhar na nGenealach, a major work of Irish genealogy, was compiled here in 1650 by Dubhaltach MacFhirbhisigh. Local legend holds that Christopher Columbus prayed in the church during a visit to Galway in 1477.