Online poker is the game of poker played over the Internet. It has been partly responsible for a dramatic increase in the number of poker players worldwide.  Online poker revenues grew from $82.7 million in 2001 to $2.4 billion in 2005, while a survey asserted online poker revenues in 2004 were at $1.4 billion.

Traditional venues for playing poker, such as casinos and poker rooms, may be intimidating for novice players and are often located in geographically disparate locations. Also, brick and mortar casinos are reluctant to promote poker because it is difficult for them to profit from it. Though the rake, or time charge, of traditional casinos is often high, the opportunity costs of running a poker room are even higher. Brick and mortar casinos often make much more money by removing poker rooms and adding more slot machines.

The major online poker sites offer varying features to entice new players. One common feature is to offer tournaments called satellites by which the winners gain entry to real-life poker tournaments. It was through one such tournament on PokerStars that Chris Moneymaker won his entry to the 2003 World Series of Poker. He went on to win the main event, causing shock in the poker world. The 2004 World Series featured three times as many players as in 2003. At least four players in the WSOP final table won their entry through an online cardroom.  Like Moneymaker, 2004 winner Greg Raymer also won his entry at the PokerStars online cardroom.