
The role-play game was started in 2004 and is set in the fictional realm of Azeroth.
Players join as weak fighters, thieves or magicians and develop their abilities online while playing against other people around the world.
Players buy the game for £19.99 ($50) in the UK and then pay around £11 ($27) per month to keep using the online world.
"We are ecstatic that the World of Warcraft community has continued to grow steadily since we launched the game," said Mike Morhaime, president and co-founder of Blizzard Entertainment, which produces the game.
"This milestone would not have been possible without the incredible support of our players."