Whiskey is made by fermenting and distilling grain, typically barley. The spelling of whiskey differs by region, with Scottish distillers using "whisky" and Irish using "whiskey". Whiskey originated in Ireland and Scotland between the 10th-15th centuries. Production involves malting, fermentation, and double distillation, with aging in oak casks for 3-15 years. The key differences between Scotch and Irish whiskey are the grains used and distillation process.