Irish orthography is the set of conventions used to write Irish. A spelling reform in the mid-20th century led to An Caighdeán Oifigiúil, the modern standard written form used by the Government of Ireland, which regulates both spelling and grammar. The reform removed inter-dialectal silent letters, simplified some letter sequences, and modernised archaic spellings to reflect modern pronunciation, but it also removed letters pronounced in some dialects but not in others.

Irish, also known as Irish Gaelic or simply Gaelic, is a Goidelic language of the Insular Celtic branch of the Celtic language group, which is a part of the Indo-European language family. Irish is indigenous to the island of Ireland and was the population's first language until the 19th century, when English gradually became dominant, particularly in the last decades of the century. Today, Irish is still commonly spoken as a first language in areas of Ireland collectively known as the Gaeltacht, in which only 2% of Ireland's population lived in 2022.