Uh, wow, I did not expect this - League of Legends has unveiled a new ranking system being added to Ranked play, dubbed the "League System." Yes, this will be very confusing, but I think I can explain it, with the help of this handy graph.
So if you're familiar with StarCraft II's ladder system, it works like that. For those who are not familiar - instead of wins adding or subtracting from a number, you gain experience for victories. When you get to 100 League Points (wins = more points, losses are less), your next game will be an advancement game. Win a series to move up a tier in your Promotion (best of five) or Division (best of three). But here's the weird thing - it works in sync with the elo system.
This is honestly pretty smart of Riot. With a progression based system, there's less frustration and anger when you lose games, which could destroy elo hell and trashtalking among teammates. Losing elo is no fun. With this, you just want to win games to get to your ladder matches. I look forward to seeing this implimented.
If you want to know more, they are hosting an AMA on Reddit this Wednesday.