If money is not an issue and you don't mind crowds, the peak tourism season--late June and July--is a fine time to visit Ireland. Temperatures average 60 degrees, and lots of tours are available.
For fewer crowds and off-season rates, fall and spring are best. Bring a rain jacket, as the weather can change many times a day during September and October. Seasonal hotels are closed from mid-November to Easter.
If you are traveling to play the greens of Ireland, mid-November to mid-February can be quite cold, wet and windy. May and September are the choicest times.
If you are interested in Ireland's biggest festivals, book in advance. The biggest St. Patrick's event is the Dublin Festival and Parade in March. The World Irish Dancing Championships are in April, the festival of traditional Irish music and dance (Fleadh Nua) is in May, and in October are the Dublin Theatre Festival and Wexford Opera Festival.
Ireland on a Whim
Say you want to travel to Ireland next month or sooner. In the spring and fall, between bed and breakfasts, hotels, hostels and country homes, you will find places to stay on short notice. In June and July, however, do not count on this.