Blizzard's rune system for Diablo III always sounded cool, but there hasn't been much of an opportunity to check it out until recently. Runes, when unlocked and activated, change the functionality of the skill they're associated with. So instead of a Monk punching multiple targets in a straight line, with the proper rune activated, the Monk can punch across a large area of effect. You can see exactly how it works in the video below...