Magic Resist

Magic resist (often shortened to "MR") is the League of Legends stat that reduces the magic damage you take, working exactly like armor but against spells instead of physical hits. Each point adds effective health versus mages and other AP threats.

It is countered by magic penetration, so heavy mages will often buy penetration to punch through it. Players build magic resist situationally, stacking it when the enemy team leans on Ability Power. Choosing the correct blend of armor and magic resist for each game is one of the clearest signs of a thoughtful, experienced player.