Difficulty Levels

Diablo III has multiple difficulty levels that you must play through to fully experience the game.

One of the major changes to D3 as compared to it's predecessors is the existence of a fourth difficulty level.

Diablo I and Diablo II both had Normal, Nightmare, and Hell difficulties. Diablo III introduces Inferno difficulty.

To progress from Normal into Nightmare requires only 2 things. You must kill Diablo for the quest reward in normal, and you must be at least level 25.

To progress from Nightmare into Hell requires that you must kill Diablo for the quest in Nightmare, and be at least level 50.

To enter Inferno difficulty, you must be at least level 60 (the current maximum level of the game), and have completed the quest to kill Diablo in Hell difficulty.

The Monster Power in which you complete the quest does not matter, so long as the quest is completed.

The following chart gives a lot of information concerning the different difficulty levels, changes imposed by Monster Power, and it's effects on your adventuring stats.