Potatoes were originally cultivated in South America. Corned beef is English. Even red hair was brought over to Ireland through waves of Viking invasions. Yet there's nothing more Irish than whiskey. In fact, the word "whiskey" comes from the Irish word for "water": uisce (pronounced ish-ka).
Translated from the Latin term aqua vitae, the "water of life," the Irish called their distilled beverage uisce beatha (pronounced ish-ka baa-ha). However, rather than distilling their uisce from grapes or other fruits (which do not grow as well in the British Isles as they do in the Mediterranean) a few enterprising monks used grains instead, as grains had proven their alcohol-producing capabilities in the production of beer.
Chief among the grains in Irish whiskey distillation is barley. Barley-based whiskies tend to have "nutty" flavors and are often described as "softer/gentler" whiskies (in comparison to the "harsher" largely corn-based whiskies of North America). Generally, the first step in making whiskey is malting the barley. The grains are soaked in water to start the germination process of the seed - this helps breakdown the starches in the seed into simpler, more-fermentable sugars. The germination process is stopped by kiln drying the grain. While you can find some "single malts" among the Irish whiskies, that term is normally associated with Scotch whisky (notice, no "e") as their barley is malted using peat-fueled fires, giving a very distinct "peaty" flavor to their malt and, subsequently, their whisky. The Irish whiskey "exception" is Connemara Peated Single Malt.
The most popular Irish whiskies, most notably Jameson and Powers, are produced by blending pot-distilled malt whiskey and column-distilled "grain" whiskey (un-malted barley, wheat, corn/maize, and/or oat). Irish whiskey is triple-distilled and then aged in oak barrels for a minimum of three years. Some distilleries will finish the aging process in Sherry barrels: Bushmills' Black Bush is a notable example. Furthermore, Midleton Very Rare is a truly exceptional blend of bourbon- and sherry-barrel aged Irish whiskies: it is remarkably smooth and has hints of tropical fruits and spice.
Single-Pot Irish Whiskies, a blend of pot-distilled barley whiskies (both malted and unmalted), are arguably the finest of the Irish whiskies. Redbreast 12 Year is an excellent example of this style of Irish whiskey. Also, while not technically an Irish whiskey (as it's produced in New York State) McKenzie's Pure Pot Still Whiskey is a great example of this style as well.
So when you celebrate "Feile Padraig" (St. Patrick's Day) this year, raise a dram of uisce beatha to your friends and family and say "Slainté" (pronounced slahn-che) – "cheers/to your health".