|This article does not cite any references or sources. (February 2011)|
The small blind is placed by the player to the left of the dealer button and the big blind is then posted by the next player to the left. The one exception is when there are only two players (a "heads-up" game), when the player on the button is the small blind, and the other player is the big blind. (Both the player and the bet may be referred to as big or small blind.)
After the cards are dealt, the player to the left of the big blind is the first to act during the first betting round. If all players call the big blind, the big blind is then given an extra opportunity to raise. This is known as a live blind. If the live blind checks, the betting round then ends.
Generally, the "big blind" is equal to the minimum bet. The "small blind" is normally half the big blind. In cases where posting exactly half the big blind is impractical due to the big blind being some odd-valued denomination, the small blind is rounded down to the nearest practical value. For example, if the big blind in a live table game is $3 then the small blind will usually be $1 or $2 since most casinos do not distribute large quantities of $0.50 poker chips.
The blinds exist because Omaha and Texas hold 'em are frequently played without antes, allowing a player to fold his hand without placing a bet. The blind bets introduce a regular cost to take part in the game, thus inducing a player to enter pots in an attempt to compensate for that expense.
It is possible to play without blinds. The minimum bet is then the lowest denomination chip in play, and tossing only one chip is considered a call. Anything higher than that is considered a raise. Poker without blinds is usually played with everyone posting an ante to receive cards.
Blinds in tournament play 
In poker tournament play, blinds serve a dual purpose. In addition to the purpose explained above, blinds are also used to control how long the tournament will last. Before the tournament begins, the players will agree to a blinds structure, usually set by the tournament organizer. This structure defines how long each round is and how much the blinds increase per round. Typically, they are increased at a smooth rate of between 25% and 50% per round over the previous round. As the blinds increase, players need to increase their chip counts (or "stacks") to stay in the game. The blinds will eventually consume all of a player's stack if he or she does not play and win more.
There are two main goals for the blinds structure:
- Ensure that by the time the desired duration of the tournament is reached, it will be very hard for players with small stacks to stay in the game. This forces players with smaller stacks to play them aggressively, thus increasing their chip count or losing everything quickly.
- Ensure that players, in general, do not have a large stack relative to the blind level.
If desired, antes can be added to further increase the pressure to win more chips.
If each player in a tournament starts with 5,000 in chips and after four hours, the big blind is 10,000 (with a small blind of 5,000), it will be very difficult for a player with only 15,000 in chips to stay in the game.