From Diablo Wiki
The Monk of Diablo III is NOT the same as Diablo I's official , but a completely new order of disciplined men and women from the country Ivgorod in the West.
The newest addition to the party will be dealing damage, but also require a alert player, or be crushed with the lack of heavy armour like the Barbarian or arcane/ancient spells like the Wizard and Witch Doctor.
Only 8 new skills were shown at BlizzCon 2008, but the Monk's signature skills gives us a very good look at how the character class will turn out.
Read more about the background, combat style and mechanic in the Monk article.