Maynooth University (MU; Irish: Ollscoil Mhá Nuad) is a constituent university of the National University of Ireland in Maynooth, County Kildare, Ireland. Maynooth University was formerly known as National University of Ireland, Maynooth (NUIM; Irish: Ollscoil na hÉireann Mhá Nuad). It was Ireland's youngest university until Technological University Dublin was established in 2019, having been founded by the Universities Act, 1997, from the secular faculties of the now separate St Patrick's College, Maynooth, which was founded in 1795. Maynooth is one of two university towns in Ireland, the other being Tralee, Co. Kerry.

The university consists of two connected campuses: an older southern campus, with 19th-century buildings, shared with St Patrick's College, and a modern northern campus, occupying c. 40 hectares (100 acres).

Over 16,000 students are enrolled in the university, employing over 1,000 staff from over 20 different countries. In 2009, Maynooth University was listed as a Top500 university in the Times Higher Education-QS World University Rankings. In 2008, it was named The Sunday Times 'University of the Year'.^{[citation needed]}

In the Times Higher Education Young University Rankings 2023, Maynooth University was ranked as the highest placed of Ireland's four universities under 50 years old.

The university and St Patrick's College, Maynooth have a common history from 1795 to 1997. The college in Maynooth was established by the government as a college for Catholic lay and ecclesiastical students in 1795. The lay college was based from 1802 in Riverstown House on the south campus. With the opening of Clongowes Wood, the lay college which had lay trustees was closed in 1817 and it functioned solely as a Catholic seminary for almost 150 years. In 1876 the college became a constituent college of the Catholic University of Ireland, and later offered Royal University of Ireland degrees in arts and science. The Pontifical Charter was granted to the college in 1896.

The college became a recognised constituent college of the National University of Ireland in 1910. From this time, arts and science degrees were awarded by the National University of Ireland, while the Pontifical University of Maynooth continued to confer its own theology degrees, as these had been prohibited in the Royal University of Ireland, and continued to the National University of Ireland (its successor) until 1997.^{[citation needed]}

In 1966 the college again allowed the entry of lay students; this greatly expanded the college and essentially set the foundation stone for Maynooth University. In 1997 the Universities Act resulted in the transfer of the faculties of arts, Celtic studies, philosophy and science of the recognised college of St Patrick's College to the new university. The university has also expanded into finance and engineering since its creation in 1997. In 2007 the university added business studies, followed by law in 2008.

Any person who was a student at St Patrick's College, Maynooth, and was conferred with a National University of Ireland degree prior to the creation of the university, is legally considered a graduate of Maynooth University.