Poker encompasses a variety of card games where players wager on which hand is the strongest based on the specific rules of the game. The game is played globally, although there may be variations in rules depending on the location. While the earliest form of poker involved only 20 cards, it is now typically played with a standard deck. However, in some countries where shorter packs are common, decks with 32, 40, or 48 cards may be used. As a result, the configuration of decks, the number of cards in play, whether they are dealt face up or face down, and how many are shared among players can all vary in poker games. Nonetheless, all variants involve one or more rounds of betting.

In most modern poker games, the initial round of betting begins with one or more players making a forced bet, such as the blind or ante. During standard poker, each player bets based on their estimation of the value of their hand compared to the other players. The action progresses in a clockwise direction, with each player having to either match the highest previous bet (or “call”) or fold, forfeiting their bets and exiting the hand. A player who matches a bet also has the option to “raise” the bet by increasing it. The betting round concludes when all players have either called the final bet or folded. If all players except one-fold during any round, the remaining player wins the pot without having to reveal their hand. If multiple players are still in the game after the final betting round, a showdown occurs, where the hands are revealed, and the player with the strongest hand claims the pot.

Except for the initial forced bets, players only voluntarily contribute money to the pot when they believe the bet has a positive expected value or when they are attempting to bluff other players for strategic reasons. Therefore, while chance plays a significant role in the outcome of any individual hand, the long-term success of players is determined by the actions they take based on probability, psychology, and game theory.

Poker has increased in popularity since the beginning of the 21st century (2001) and has gone from being primarily a recreational activity confined to small groups of enthusiasts to a widely popular activity, both for participants and spectators, including online, with many professional players and multimillion-dollar tournament prizes.“

“n the game of poker, the play largely centers on the act of betting, and as such, a protocol has been developed to speed up play, lessen confusion, and increase security while playing. Different games are played using different types of bets, and small variations in etiquette exist between cardrooms, but for the most part the following rules and protocol are observed by the majority of poker players.

Players in a poker game act in turn, in clockwise rotation (acting out of turn can negatively affect other players). When it is a player's turn to act, the first verbal declaration or action they take binds them to their choice of action; this rule prevents a player from changing their action after seeing how other players react to their initial action.

Until the first bet is made each player in turn may “check”, which is to not place a bet, or “open”, which is to make the first bet. After the first bet each player may “fold”, which is to drop out of the hand losing any bets they have already made; “call”, which is to match the highest bet so far made; or “raise”, which is to increase the previous high bet.

A player may fold by surrendering one's cards. (Some games may have specific rules regarding how to fold: for example in stud poker one must turn one's upcards face down.) A player may check by tapping the table or making any similar motion. All other bets are made by placing chips in front of the player, but not directly into the pot (“splashing the pot” prevents other players from verifying the bet amount).

Play proceeds to the left of the dealer

In general, the person to the left of the dealer acts first and action proceeds in a clockwise fashion. If any player has folded earlier, action proceeds to next player. In games with blinds, the first round of betting begins with the player to the left of the blinds. In stud games, the action begins with the player showing the strongest cards and proceeds clockwise. If there is a bring-in, the first round of betting begins with the player obliged to post the bring-in.

Check

If no one has yet opened the betting round, a player may pass or check, which is equivalent to betting zero and/or to call the current bet of zero. When checking, a player declines to make a bet; this indicates that they do not wish to open, but do wish to keep their cards and retain the right to call or raise later in the same round if an opponent opens. In games played with blinds, players may not check on the opening round because the blinds are live bets and must be called or raised to remain in the hand. A player who has posted the big blind has the right to raise on the first round, called the option, if no other player has raised; if they decline to raise they are said to check their option. If all players check, the betting round is over with no additional money placed in the pot (often called a free round or free card). A common way to signify checking is to tap the table, either with a fist, knuckles, an open hand or the index finger(s).

Open, bet, raise

If in any betting round it is a player's turn to act and the action is unopened, then the player can open action in a betting round by making a bet—the act of making the first voluntary bet in a betting round is called opening the round. On the first betting round, it is also called opening the pot, though in variants where blind bets are common, the blind bets “open” the first betting round and other players call and/or raise the “big blind” bet. Some poker variations have special rules about opening a round that may not apply to other bets. For example, a game may have a betting structure that specifies different allowable amounts for opening than for other bets, or may require a player to hold certain cards (such as “Jacks or better”) to open.

The pot of chips is normally kept in the center of the table

Normally, a player makes a bet by placing the chips they wish to wager into the pot. Under normal circumstances, all other players still in the pot must either call the full amount of the bet or raise if they wish to remain in, the only exceptions being when a player does not have sufficient stake remaining to call the full amount of the bet (in which case they may either call with their remaining stake to go “all-in” or fold) or when the player is already all-in.

To raise is to increase the size of an existing bet in the same betting round. A player making the second (not counting the open) or subsequent raise of a betting round is said to re-raise. A player making a raise after previously checking in the same betting round is said to check-raise. The sum of the opening bet and all raises is the amount that all players in the hand must call in order to remain eligible to win the pot, subject to the table stakes rules described in the previous paragraph.

A bluff is when a player bets or raises when it is likely they do not have the best hand; it is often done in hopes that (an) opponent(s) will fold mediocre yet stronger hands. When a player bets or raises with a weak hand that has a chance of improvement on a later betting round, the bet or raise is classified as a semi-bluff. On the other hand, a bet made by a player who hopes or expects to be called by weaker hands is classified as a value bet.

In no-limit and pot-limit games, there is a minimum amount that is required to be bet in order to open the action. In games with blinds, this amount is usually the amount of the big blind. Modern poker rules require that raises must be at least equal to the amount of the previous bet or raise. For example, if an opponent bets $5, a player must raise by at least another $5, and they may not raise by only $2. If a player raises a bet of $5 by $7 (for a total of $12), the next re-raise would have to be by at least another $7 (the previous raise) more than the $12 (for a total of at least $19). The primary purpose of the minimum raise rule is to avoid game delays caused by “nuisance” raises (small raises of large bets, such as an extra $1 over a current bet of $50, that have little effect on the action but take time as all others must call). This rule is overridden by table stakes rules, so that a player may in fact raise a $5 bet by $2 if that $2 is their entire remaining stake. The only exception is if someone goes all in for less than a legal raise. For example, if the minimum bet is $5 and a player goes all in for $4, the next player can call the $4; if they want to raise, they would have to make it $9 ($4 plus the minimum bet).

In no-limit and pot-limit games, if a player opens action in a betting round by placing any number of chips in the pot without a verbal declaration, or if they place two or more chips in the pot of sufficient value to raise an outstanding bet or raise without a verbal declaration, then the full amount placed in the pot will be assumed to be the amount of the bet or raise. Sometimes, a player will not have enough chips in smaller denominations that would be needed to make a bet or raise in the desired amount—for example, a player may be out of $1 and $5 chips and still have $25 chips—if the pot is currently $70 and the player wants to open action by betting half the pot, they will want to bet $35. In such cases, instead of slowing down the game by asking the dealer or another player to provide “change” a player may simply verbally declare the amount they are betting while placing (a) chip(s) of sufficient value to make good on the bet. Any “change” will be returned to them by the dealer if necessary.

Also in no-limit and pot-limit games, a raise may be expressed as either a raise by $X or a raise to $X. For example, suppose Alice opens by betting $5. If Dianne subsequently announces “I raise by $15” she will be raising by $15 over and above the opening bet of $5, for a total bet of $20. On the other hand, if Dianne subsequently announces “I raise to $15” she will be raising by only $10 for a total bet of $15. Today, most public cardrooms prefer for players to use the raise to standard as opposed to the raise by standard. In the event of any ambiguity in a player's verbal action while raising, the player will normally be bound to raise to the stated amount. For example, if Alice were to have opened with a $5 bet and Dianne subsequently announced “raise, $15” while putting $15 into pot (making the pot $20), in most public cardrooms Dianne would be bound to a total bet of $15 and the “excess” $5 would be returned to her.

In fixed-limit games, the size of bets and raises is determined by the specified stakes. For example, in $3/$6 fixed limit Hold 'em, during the first two betting rounds (preflop and flop) the big blind is $3, the opening bet after the flop must be for $3 and all raises must be for $3. For the last two betting rounds (turn and river) the opening bet must be for $6 and all raises must be for $6. As in no-limit and pot-limit games, these amounts will be over-ridden by table stakes rules (so for example, in $3/$6 fixed limit Hold 'em a player could bet, raise or call for only $2 at any time if that is their remaining stake).

Also, in fixed-limit and spread-limit games most casinos cap the total number of raises allowed in a single betting round (typically three or four, not including the opening bet of a round). For example, in a casino with a three-raise rule, if one player opens the betting for $5, the next raises by $5 making it $10, a third player raises another $5, and a fourth player raises $5 again making the current bet $20, the betting is said to be capped at that point, and no further raises beyond the $20 level will be allowed on that round. It is common to suspend this rule when there are only two players betting in the round (called being heads-up), since either player can call the last raise if they wish. Pot-limit and no-limit games do not have a limit on the number of raises.

If, because of opening or raising, there is an amount bet that the player in-turn has not paid, the player must at least match that amount, or must fold; the player cannot pass or call a lesser amount (except where table stakes rules apply).

Call

To call is to match a bet or match a raise. A betting round ends when all active players have bet an equal amount. If no opponents call a player's bet or raise, the player wins the pot.

The second and subsequent calls of a particular bet amount are sometimes called overcalls. This term is also sometimes used to describe a call made by a player who has put money in the pot for this round already. A player calling a raise before they have invested money in the pot in that round is cold calling. For example, if in a betting round, Alice bets, Dianne raises, and Carol calls, Carol “calls two bets cold”. A player calling instead of raising with a strong hand is smooth calling or flat calling, a form of slow play.

Calling in the final betting round when a player thinks they do not have the best hand is called a crying call. Calling when a player has a relatively weak hand but suspects their opponent may be bluffing is called a hero call. Calling a bet prior to the final betting round with the intention of bluffing on a later betting round is called a float.

In public cardrooms, placing a single chip in the pot of any value sufficient to call an outstanding bet or raise without a verbal action declaring otherwise always constitutes a call. If necessary, any “change” from the chip will be returned to the player at the end of the betting round, or perhaps even sooner if this can conveniently be done. If, when it is a player's turn to act, the player already has an oversized chip in the pot that has not yet been “changed” and that is of sufficient value to call an outstanding bet or raise, then the player may call by tapping the table as if checking.

In public cardrooms and casinos where verbal declarations are binding, the word “call” is such a declaration. In public card rooms, the practice of saying “I call, and raise $100” is considered a string raise and is not allowed. Saying “I call” commits the player to the action of calling, and only calling.

Note that the verb “see” can often be used instead of “call”: “Dianne saw Carol's bet”, although the latter can also be used with the bettor as the object: “I'll see you” means 'I will call your bet'. However, terms such as “overseeing” and “cold seeing” are not valid.

Fold

To fold is to discard one's hand and forfeit interest in the current pot. No further bets are required by the folding player, but the player cannot win. Folding may be indicated verbally or by discarding one's hand face down into the pile of other discards called the muck, or into the pot (uncommon). For this reason it is also called mucking. In stud poker played in the United States, it is customary to signal folding by turning all of one's cards face down. Once a person indicates a fold or states I fold, that person cannot re-enter the hand. In casinos in the United Kingdom, a player folds by giving their hand as is to the “house” dealer, who spreads the cards face up for the other players to see before mucking them.”

Action and betting

When participating in the hand, a player is expected to keep track of the betting action. Losing track of the amount needed to call, called the bet to the player, happens occasionally, but multiple occurrences of this slow the game down and so it is discouraged. The dealer may be given the responsibility of tracking the current bet amount, from which each player has only to subtract their contribution, if any, thus far.

To aid players in tracking bets, and to ensure all players have bet the correct amount, players stack the amount they have bet in the current round in front of them. When the betting round is over (a common phrase is “the pot's good”), the players will push their stacks into the pot or the dealer will gather them into the pot. Tossing chips directly into the pot (known as splashing the pot), though popular in film and television depictions of the game, causes confusion over the amount of a raise and can be used to hide the true amount of a bet. Likewise, string raises, or the act of raising by first placing chips to call and then adding chips to raise, causes confusion over the amount bet. Both actions are generally prohibited at casinos and discouraged at least in other cash games.

Acting out of turn

Most actions (calls, raises or folds) occurring out-of-turn—when players to the right of the player acting have not yet made decisions as to their own action—are considered improper, for several reasons. First, since actions by a player give information to other players, acting out of turn gives the person in turn information that they normally would not have, to the detriment of players who have already acted.

For instance, say that with three players in a hand, Player A has a weak hand but decides to try a bluff with a large opening bet. Player C then folds out of turn while Player B is making up their mind. Player B now knows that if they fold, A will take the pot, and also knows that they cannot be re-raised if they call. This may encourage Player B, if they have a good “drawing hand” (a hand currently worth nothing but with a good chance to improve substantially in subsequent rounds), to call the bet, to the disadvantage of Player A.

Second, calling or raising out of turn, in addition to the information it provides, assumes all players who would act before the out of turn player would not exceed the amount of the out-of-turn bet. This may not be the case, and would result in the player having to bet twice to cover preceding raises, which would cause confusion.

Cards

Players work to minimize the visibility of their hand to others by only turning up part of their cards. A player is never required to expose their concealed cards when folding or if all others have folded; this is only required at the showdown.

Many casinos and public cardrooms using a house dealer require players to protect their hands. This is done either by holding the cards or, if they are on the table, by placing a chip or other object on top. Unprotected hands in such situations are generally considered folded and are mucked by the dealer when the action reaches the player. This can spark heated controversy and is rarely done in private games.

The style of game generally determines whether players should hold face-down cards in their hands or leave them on the table. Holding “hole” cards allows players to view them more quickly and thus speeds up gameplay, but spectators watching over a player's shoulder can communicate the strength of that hand to other players, even unintentionally. Unwary players can hold their hand such that a “rubbernecker” in an adjacent seat can sneak a peek at the cards. Lastly, given the correct light and angles, players wearing glasses can inadvertently show their opponents their hole cards through the reflection in their glasses. Thus for most poker variants involving a combination of faceup and facedown cards (most variants of stud and community are dealt in this manner), the standard method is to keep hole cards face-down on the table except when it is that player's turn to act. Five-card draw is generally played with hands held by the players at all times.

Cash and chips

Chips are available in many denominations. Making change out of the pot is allowed in most games; to avoid confusion, the player should announce their intentions first. Then, if opening or cold calling, the player may exchange a large chip for its full equivalent value out of the pot before placing their bet, or if over-calling may place the chip (announcing that they are calling or raising a lesser amount) and remove the change from their own bet for the round. Normally, if a player places one oversized chip in the pot without explicitly voicing intention while facing a bet, the action is automatically deemed a call whether or not the chip is large enough to otherwise qualify as a raise. In most casinos players are prohibited from handling chips once they are placed in the pot, although a player removing their own previous bet in the current round from the pot for the purpose of calling a raise (or re-raising) is usually tolerated. Otherwise, the dealer is expected to make change when required.

Making change should, in general, be done between hands whenever possible, when a player sees they are running low of an oft-used value. The house dealer at most casinos maintains a chip bank and can usually make change for a large amount of chips. In informal games, players can make change with each other or with unused chips in the set. While this can prevent delays while players figure out change for a bet, casinos generally frown on or outright prohibit such practices to prevent players from surreptitiously “ratholing” (taking away and securing part of the stakes for personal use) and/or circumventing buy-in limits. Similarly, buying in for an additional amount must be done between hands (or, at least, done after a player has folded during the current hand) since players are not allowed to add to their stack during a hand. If buy-ins cannot and/or are not expected to be handled by the dealer it can take two or three hands for an attendant to bring another tray to the table. As described below, some casinos alleviate this issue by allowing cash to be deemed temporarily “in play” while staff fetches chips. Players who wish to always play with at least the buy-in limit will often carry additional chips in their pocket so that whenever they lose a pot they can quickly “top up” without inconveniencing the dealer or delaying the game.

While having players buy chips directly from the dealer is seen as a convenience by some players, and can help deter players from exceeding buy-in limits, many players dislike this system because it slows down the game, especially if the dealer is expected to count large numbers of small denominations of chips. Also, many jurisdictions require all such purchases (or, at least, all larger transactions) to be confirmed (primarily to ensure accuracy) by a supervisor or other staff member, potentially causing further delay. To speed up play (and, by extension, increase the number of hands dealt and rake earned by the casino), many casinos require players to buy chips from a cashier - to assist players, some establishments employ chip runners to bring cash and chips to and from the tables. Many casinos have a dedicated cashier station located in or very near the poker room, although in some (usually, smaller venues) the same cashier station that handles other transactions will also handle poker-related purchases. In addition, if the casino uses the same chips for poker as for other games then it is often possible to bring chips from such games to the poker table.

Touching another player's chips without permission is a serious breach of protocol and can result in the player being barred from the casino.

Most tournaments and many cash games require that larger denomination chips be stacked in front (i.e., closer to the center of the table, or closer to the pot) of the player's lesser denomination chips, or at least stacked in such a manner that they can be easily seen by all opponents. This rule is employed to discourage attempts to conceal stack size. Some casinos discourage, prohibit or simply refrain from circulating larger chip denominations to prevent them from being used in lower-stakes cash games, although the drawback is that larger stacks won during play will become more difficult to handle and manage as a result.

Some informal games allow a bet to be made by placing the amount of cash on the table without converting it to chips, as this speeds up play. However, table stakes rules strictly prohibit this from being done while a hand is in progress. Other drawbacks to using cash include the ease with which cash can be “ratholed”, which is normally disallowed, in addition to the security risk of leaving cash on the table. As a result, many games and virtually all casinos require a formal “buy-in” when a player wishes to increase their stake, or at least require any cash placed on the table to be converted into chips as quickly as possible.

Players in home games typically have both cash and chips available; thus, if money for expenses other than bets is needed, such as food, drinks and fresh decks of cards, many players typically pay out of pocket. Some players (especially professionals) loathe removing any part of their stack from play for any reason, especially once their stacks exceed the initial buy-in limit. In casinos and public cardrooms, however, the use of cash is occasionally restricted or discouraged, so players often establish a small cache of chips called the “kitty”, used to pay for such things. Players contribute a chip of lowest value towards the kitty when they win a pot, and it pays for expenses other than bets such as tipping the dealer as well as (where applicable) to pay for “rent” (formally known as time fees) and/or buying fresh decks of cards (while many public cardrooms include such costs in the “rake” or other fees, some charge separately for such things as playing cards and “rent”), and similar costs. At a casino, dealers who exchange cash for chips are expected to immediately secure any cash by placing it into a locked box near their station. This means that regardless of how chips are purchased, when cashing them in it is typically not possible to sell them back to the dealer since they have no access to any cash. Poker chips must therefore be taken to the cashier to be exchanged for cash. Dealers who handle buy-ins will often be willing (and sometimes encourage) departing players to “color up” their stacks by exchanging them for the highest-available denominations, both for the convenience of the player and to minimize the number of times casino staff must deliver fresh chips to the poker table - a time-consuming process. On the other hand, casinos that expect players to buy chips from the cashier will usually furnish players with chip trays (typically designed to handle 100 chips each) to ease the handling of large numbers of chips.

Chips given by players or otherwise retained by the dealer for tips, rake and other fees (where applicable) are usually placed in separate locked boxes by the dealer, although in some casinos the rake is kept in a separate row in the dealer's tray.

Other rules

Public cardrooms often have additional rules designed to speed up play, earn revenue for the casino (such as the “rake”), improve security and discourage cheating.”

In casual play, the right to deal a hand typically rotates among the players and is marked by a token called a dealer button (or buck). In a casino, a house dealer handles the cards for each hand, but the button (typically a white plastic disk) is rotated clockwise among the players to indicate a nominal dealer to determine the order of betting. The cards are dealt clockwise around the poker table, one at a time.

One or more players are usually required to make forced bets, usually either an ante or a blind bet (sometimes both). The dealer shuffles the cards, the player on the chair to their right cuts, and the dealer deals the appropriate number of cards to the players one at a time, beginning with the player to their left. Cards may be dealt either face-up or face-down, depending on the variant of poker being played. After the initial deal, the first of what may be several betting rounds begins. Between rounds, the players' hands develop in some way, often by being dealt additional cards or replacing cards previously dealt. At the end of each round, all bets are gathered into the central pot.

At any time during a betting round, if one player bets, no opponents choose to call (match) the bet, and all opponents instead fold, the hand ends immediately, the bettor is awarded the pot, no cards are required to be shown, and the next hand begins. This is what makes bluffing possible. Bluffing is a primary feature of poker, distinguishing it from other vying games and from other games that use poker hand rankings.

At the end of the last betting round, if more than one player remains, there is a showdown, in which the players reveal their previously hidden cards and evaluate their hands. The player with the best hand according to the poker variant being played wins the pot. A poker hand comprises five cards; in variants where a player has more than five cards available to them, only the best five-card combination counts. There are 10 different kinds of poker hands, such as straight flush and four of a kind.

Poker has many variations, all following a similar pattern of play and generally using the same hand ranking hierarchy. There are four main families of variants, largely grouped by the protocol of card-dealing and betting:

A complete hand is dealt to each player, and players bet in one round, with raising and re-raising allowed. This is the oldest poker family; the root of the game as now played was a game known as Primero, which evolved into the game three-card brag, a very popular gentleman's game around the time of the American Revolutionary War and still enjoyed in the U.K. today. Straight hands of five cards are sometimes used as a final showdown, but poker is almost always played in a more complex form to allow for additional strategy.

Cards are dealt in a prearranged combination of face-down and face-up rounds, or streets, with a round of betting following each. This is the next-oldest family; as poker progressed from three to five-card hands, they were often dealt one card at a time, either face-down or face-up, with a betting round between each. The most popular stud variant today, seven-card stud, deals two extra cards to each player (three face-down, four face-up) from which they must make the best possible 5-card hand.

Five-card draw: A complete hand is dealt to each player, face-down. Then each player must place an ante to the pot. They can then see their cards and bet accordingly. After betting, players can discard up to three cards and take new ones from the top of the deck. Then, another round of betting takes place. Finally, each player must show their cards and the player with the best hand wins.

Also known as “flop poker,” community card poker is a variation of stud poker. Players are dealt an incomplete hand of face-down cards, and then a number of face-up community cards are dealt to the center of the table, each of which can be used by one or more of the players to make a 5-card hand. Texas hold 'em and Omaha are two well-known variants of the community card family.

There are several methods for defining the structure of betting during a hand of poker. The three most common structures are known as “fixed-limit,” “pot-limit,” and “no-limit.” In fixed-limit poker, betting and raising must be done by standardized amounts. For instance, if the required bet is X, an initial bettor may only bet X; if a player wishes to raise a bet, they may only raise by X. In pot-limit poker, a player may bet or raise any amount up to the size of the pot. When calculating the maximum raise allowed, all previous bets and calls, including the intending raiser's call, are first added to the pot. The raiser may then raise the previous bet by the full amount of the pot. In no-limit poker, a player may wager their entire betting stack at any point that they are allowed to make a bet. In all games, if a player does not have enough betting chips to fully match a bet, they may go “all-in,” allowing them to show down their hand for the number of chips they have remaining.

James Garner as fictional poker player Bret Maverick and Jack Kelly as his brother Bart Maverick from the 1957 television series Maverick

While typical poker games award the pot to the highest hand as per the standard ranking of poker hands, there are variations where the best hand, and thus the hand awarded the pot, is the lowest-ranked hand instead. In such games the best hand contains the lowest cards rather than the highest cards; some variations may be further complicated by whether or not hands such as flushes and straights are considered in the hand rankings. There are also games where the highest and lowest hands divide the pot between them, known as “high low split,” games.

Other games that use poker hand rankings may likewise be referred to as poker. Video poker is a single-player video game that functions much like a slot machine; most video poker machines play draw poker, where the player bets, a hand is dealt, and the player can discard and replace cards. Payout is dependent on the hand resulting after the draw and the player's initial bet.

Strip poker is a traditional poker variation where players remove clothing when they lose their bets. Since it depends only on the basic mechanic of betting in rounds, strip poker can be played with any form of poker; however, it is usually based on simple variants with few betting rounds, like five cards draw.

Another game with the poker name, but with a vastly different mode of play, is called Acey-Deucey or Red Dog poker. This game is more similar to Blackjack in its layout and betting; each player bets against the house, and then is dealt two cards. For the player to win, the third card dealt (after an opportunity to raise the bet) must have a value in-between the first two. Payout is based on the odds that this is possible, based on the difference in values of the first two cards. Other poker-like games played at casinos against the house include three card poker and pai gow poker.

A variety of computer poker players have been developed by researchers at the University of Alberta, Carnegie Mellon University, and the University of Auckland amongst others.

In a January 2015 article published in Science, a group of researchers mostly from the University of Alberta announced that they “essentially weakly solved” heads-up limit Texas Hold 'em with their development of their Cepheus poker bot. The authors claimed that Cepheus would lose at most 0.001 big blinds per game on average against its worst-case opponent, and the strategy is thus so “close to optimal” that “it can't be beaten with statistical significance within a lifetime of human poker playing.”

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