Long before Guinness brewed its first pint of stout, and centuries before Americans started adding green food coloring to their beer (or, in some cases, milk) every March 17, Ireland gave birth to what many consider that nation's signature tipple: whiskey. While Guinness may be good for you, according to its classic slogan, the name of the Emerald Isle's more potent potable comes from the Gaelic for "water of life."
Further bolstering the case for whiskey as the most appropriate choice for St. Patrick's Day alcohol consumption is the (probably unreliable) legend that claims the process of distillation was introduced to Ireland by none other than the saint himself. While no one knows for sure when whiskey made its debut, it is usually accepted that it originated in Ireland sometime in the Middle Ages—the first whiskey distillery licensed in the British Isles was Bushmills, in Northern Ireland, in 1608—before spreading to Scotland and, later, to the United States and Canada.
What makes Irish whiskey different from the products of those countries? For one thing, spelling. For reasons that, according to The Glutton's Glossary by John Ayto, probably had to do with marketing rather than language differences, around the end of the 19th century it became standard that the Irish (and Americans) make whiskey and Scots (and Canadians) make whisky.
But more than an "e" distinguishes Irish whiskey from Scotch. Irish whiskey is made with a blend of malted and unmalted barley in the pot still phase, whereas Scotch uses only malted barley (grain that has been soaked so that it begins to sprout). Also, the malted barley in Scotch is dried over peat smoke, which gives it a distinctive flavor; Irish whiskey, which is made from kiln-dried barley, tastes more of the grain itself.
Finally, unlike Scotch, which is distilled twice, Irish whiskey is usually triple-distilled, which results in a smoother, higher-alcohol spirit. This practice was introduced by John Jameson, a Scottish transplant who established one of Ireland's most successful whiskey distilleries, in 1780.
In order to appreciate the subtleties of flavor, the aficionado drinks Irish whiskey neat, or with a bit of water, which is supposed to bring out the liquor's hidden characteristics. Of course, it also goes nicely in an Irish coffee.
Not being an aficionado myself, my favorite way to have whiskey is baked in a dessert, like this bittersweet chocolate Irish whiskey cake, where its bite nicely balances out the sweetness.