Displayed beneath each player’s ranking medal, you will find a number that corresponds to a player's MMR (matchmaking rating). The MMR is a sort of quantification of the overall skill level of a player. The difference between the medal and the MMR is the fact that unlike the medal, the MMR fluctuates freely and changes after each match. If the player loses a match, he loses 25 MMR points, if he wins, 25 points will be added to his MMR.
IMPORTANT! New accounts that have never received a rank before, will receive a maximum of 3,500 MMR points. Players who are better than 3,500 MMR will have to win matches in order for their MMR to be higher and for them to get into higher tier matches.
In Dota 2, a player's MMR is private (hidden from other players) and only visible to the owner of the account. Therefore, a player can only track his own MMR and not the MMR of his fellow players. Furthermore, Valve has been quite secretive about their methods of matching players into leagues and the ways in which the MMR is taken into account. No one knows the exact formulas used by Valve for the matchmaking system. It is also worth mentioning that MMR is not the only thing that influences a player's medal. We know this because there are many examples of players who have received medals that are far above their MMR range.
What are your thoughts about Valve's ranking system? Are you happy with the current matchmaking system?