Irish Gaelic lexicography began in the seventh century, and the Irish have been fascinated with their native language ever since. From pseudo-etymological glossaries, hard-word glossaries appeared, but the first complete vocabulary was Risdeard Pluincéad’s Latin-Irish manuscript dictionary of 1662, part of the project of Irish Franciscans who wished to represent Ireland as a modern nation. Part of Pluincéad’s dictionary was incorporated into Edward Lhuyd’s Archaeolgia Britannica of 1707, which included the first published Irish-English dictionary. In the eighteenth century Irish-English and English-Irish dictionaries appeared, but the most widely used dictionary, the O’Reilly series (1817–77), omitted many common words. Dinneen produced his first Irish-English dictionary in 1904 and a greatly enlarged version in 1927. This is still very useful. The English-Irish dictionaries of O’Neill-Lane and McKenna are also helpful. In 1957 de Bhaldraithe produced a Modern English-Irish dictionary. The dictionary of Old and Middle Irish was completed in 1976, and in 1977, Ó Dónaill made his Modern Irish-English dictionary. Irish dialect dictionaries and electronic resources are also discussed.