More than 3,000 people of all ages will take part in competitions, but thousands more will attend impromptu music sessions and concerts at different venues around the Co Kerry town.
Open-air events will centre around a gig-rig in Main St, starting tonight with an Uí Bhríain céilí, to be followed by other performances throughout the weekend.
Indoor events will feature Four Men and a Dog, supported by TG4 Young Musician of the Year Bryan O’Leary, in the Gleneagle Hotel, tomorrow night.
Saturday and Sunday are the main competition days, with St Brendan’s College, Presentation Monastery, and Killarney Community College being the venues.
Céilí and set dancing competitions will be held in the Gleneagle Hotel for people under the age of 15 to seniors.
The fleadh, which has Kerry Group as its main sponsor, will finish on Sunday night with a free performance by Celtic Steps on the gig-rig.
Last night’s official opening was performed by Comhaltas Ceoltóirí Éireann director general, Labhrás Ó Murchú.
With the annual July Races also under way and the tourist season reaching its peak, Killarney will be chock-a-block and pub cash registers will merrily beat to the sound of fiddles, banjos, and bodhráns.
Meanwhile, large numbers of stylish women will attend Ladies Day at the races today where the fashion competition judges will be television presenter Kathryn Thomas and Rose of Tralee Haley O’Sullivan.