Ireland punches well above its weight for festivals, with a particular strength in traditional music, literature, and food.
St Patrick's Day (17 March) is celebrated everywhere in the country, but the Dublin parade is the biggest, drawing large crowds. The festival runs for several days. It's the height of tourist season for a few days in what is otherwise a quiet time of year — book accommodation far ahead if you plan to be in Dublin.
Fleadh Cheoil (August/September) is the all-Ireland traditional music championship, held in a different town each year. It attracts tens of thousands of musicians and visitors, with sessions spilling out of pubs onto the streets. If you happen to be in Ireland when Fleadh is on, it's worth going out of your way for.
Galway International Arts Festival (July) is a two-week programme of theatre, visual art, music, and street performance. Galway during the Arts Festival is genuinely electric, with outdoor events making the most of the city's compact streets.
Galway Oyster Festival (September) celebrates the start of the oyster season with tastings, an international oyster-opening competition, and a great deal of Guinness. One of the most enjoyable food events in the country.
Kilkenny Arts Festival (August) is one of the best-established arts festivals in Ireland, with a strong programme of classical music, visual art, and theatre in Kilkenny's medieval setting.
Cork Jazz Festival (October) brings international and Irish jazz acts to Cork over the October bank holiday weekend. The city fills up; book early.
Wexford Opera Festival (October/November) is a long-running and internationally respected event that focuses on rarely performed operas. Wexford Town is otherwise a quiet place, which makes the contrast during festival week all the more enjoyable.
TradFest Dublin (January) is an increasingly prominent festival of traditional Irish music held in Dublin venues including Malahide Castle and St Patrick's Cathedral — a good reason to visit in the quiet winter season.