The rules of Gin Rummy are similar to those of Rummy. The main difference is that the players do not lay down their sets and runs until they are prepared to end the round. If the opposing player has valid runs or sets in his hand, they will not count as points.
Each player is dealt 10 cards. The dealer then places the remaining cards facedown, creating the stockpile, and turns the top card face up next to it, creating the discard pile.
Play goes around the table to the left. Each player takes a turn, either taking a face-up card from the discard pile or a facedown card from the stockpile. The player adds this card to his hand and discards another. He may not discard the one he has drawn until the next hand.
Each player is trying to meld runs and sets in his hand. A run is a sequence of at least 3 consecutive cards in the same suit (10♣, J♣, Q♣, K♣). A set is a group of at least 3 cards of the same number (5♥, 5♣, 5♠).
A player can end the round, or “knock,” by placing his discard face-down when he has completed enough melds that his “deadwood” (the cards in his hand, not counting melds) totals fewer than 10 points. Points are determined by the face value of each card held, with Aces worth 1 and face cards worth 10 each. If a player can complete his hand without any deadwood, he discards his last card face-down and declares “Gin” and earns a 25-point bonus, in addition to his opponent’s deadwood points.
When a player ends a round by knocking, his opponents lay down all their valid runs and sets. Opponents may also lay off their other cards on the player’s melds if the addition makes a valid meld. Whatever cards remain are scored.
When a player ends a round by going Gin, the same rules apply, except the opponent cannot lay off his cards on the player’s melds. This makes for a higher deadwood point count — and significant incentive to hold out and try to Gin.
Players agree beforehand on a winning amount of points, typically 100.
Mix it up
Come up with family rules of your own. In one version of Gin Rummy, the card flipped face-up to start the round sets the deadhead point-limit for knocking. In another, if a spade is flipped up to start the round, then that round is worth double the points.