From Diablo Wiki
Intelligence is one of the core attributes for characters in Diablo III. It governs how much Life a character gains from Health Globes and increases Witch Doctor's and Wizard's damage dealt as their mainstat.
Each point of Intelligence grants:
- +0.1 per point to Resistances. (Thus 10 points of INT = 1 point of resistance for all classes.)
- +1% to Witch Doctor's damage.
- +1% to Wizard's damage.
Intelligence is a new attribute that was introduced in 2012's attribute overhaul. Diablo I had Magic, Diablo II had Energy and in early development Diablo III had Willpower. Intelligence hasn't been used in Diablo games before and it's not known why Blizzard chose to pick a new name for this stat.