Aside from the obvious geographical differences (Irish whiskey must be made in Ireland, Scotch in Scotland!), there are some key production differences between most Irish and Scotch whiskies. Check out ‘What is Scotch whisky?’ first for the Scotch specifics.
Firstly, most Irish whiskeys are a blend of pot- and column-distilled spirits. Irish whiskey has an additional category called single pot still, where unmalted barley is used along with malted barley for oilier, fruitier flavours. Irish single malt or single pot still whiskey is also largely triple distilled, whereas single malt Scotch whisky is typically only pot-distilled twice.
Irish whiskey also has single malt, single grain and blended whiskey categories.