In Diablo 3 for the PC, the Inferno difficulty is the fourth and final difficulty in the game. I hope you’re prepared for this one, because it’s far from easy, even at max level with good gear.
To unlock the Inferno difficulty, you just need to complete all Acts on the Hell difficulty, and reach level 60.
Check out my other article if you’re trying to figure out how to unlock the other difficulties in Diablo 3.