Fizzbin was a card game said to originate from Beta Antares IV, despite Spock's protests to the contrary. Captain James T. Kirk invented this game to free himself, his first officer, Spock, and his chief medical officer, Leonard McCoy, from captivity at the hands of a group of Iotians who had mimicked early 20th century Earth-style gangsters.
While Kirk was explaining the extremely convoluted rules of the game to his captors, he used what he called the last card, the "kronk," as a distraction to knock the captors unconscious. McCoy and Spock then escaped back to the USS Enterprise. (TOS: "A Piece of the Action")
The rules for fizzbin were intended to be complex, so that Kirk could lull his audience into lowering their defenses long enough to be overwhelmed.
- The game can be played with a standard Earth deck of cards, despite the slightly differing deck on Beta Antares IV.
- How many players can take part is not specified, but four is apparently the usual number. Judging from the way Kirk dealt the cards, dealing always progresses clockwise.
- Each player gets six cards, except for the player on the dealer's right, who gets seven.
- The second card is turned up, except on Tuesdays.
- Two jacks are a "half-fizzbin."
- If you have a half-fizzbin:
- A third jack is a "sralk" and results in disqualification, however if the jack is dealt on progress towards a royal fizzbin, it is considered a very lucky hand;
- One wants a king and a deuce, except at night, when one wants a queen and a four;
- If a king had been dealt, the player would get another card, except when it is dark, in which case he would have to forfeit that card.
- The top hand is a "royal fizzbin," but the odds against getting one are said to be "astronomical." Spock admitted, "I've never computed them."
The idea of suggesting fizzbin, spontaneously created by Captain Kirk, had since become a real game was devised by Ira Steven Behr and Robert Hewitt Wolfe, while they wrote "The Ascent." (Star Trek: Deep Space Nine Companion, p. 403.) It was never explained how a game seemingly invented on the spot by Kirk could have spread to other parts of the galaxy by the next century. Referring to Quark's awareness of the game, Ronald D. Moore commented, perhaps tongue-in-cheek, "Kirk evidently marketed this game after he brought the original Enterprise home." (AOL chat, 1997) Ira Behr and Robert Wolfe had a different explanation, though. "We figured that the people on Sigma Iotia II [...] were able to extrapolate a game from the little bit that Kirk told them," recalled Wolfe. "Now it's the national game of Iotia and Quark knows how to play it." (Star Trek: Deep Space Nine Companion, p. 403.) The authors of the Star Trek Encyclopedia wrote: "It seems unusual that Quark would know of Kirk's bluff, but then again, maybe Quark (like Sisko) was a fan of the legendary starship captain".
According to the script for "The Ascent," fizzbin was pronounced as "FIZZ-bin." 
In the Nintendo game Star Trek: 25th Anniversary, you must win back McCoy's communicator by playing a game of fizzbin. The hand you need to win is called a supernova.
In The Empty Chair, the final Rihannsu novel by Diane Duane, McCoy comes up with "tournament fizzbin" after their Romulan ally Ael t'Rllaillieu has trouble understanding poker. The game consists entirely of the participants making up the rules as they go along and drinking copious amounts of Romulan ale.