The origin of the game can be traced back to a 17^th century game called Conquian which was played in Central American states such as Mexico. It is believed that it is merely a modified version of Conquian with different rules and scoring methods. For this reason, Conquian is often called the prototype of the game.

One of the reasons why the history of Gin Rummy remains tantalisingly obscure is that it didn’t really come into its own until the 1930s, for as late as the 1926 edition of Official Rules of Card Games it was still being recorded under its older title Poker Gin or Gin Poker. One circumstance that helped it was the Depression, when more and more people had less and less to spend on going out and enjoying themselves and had to rediscover the art of amusing themselves at home. Gin was much simpler to learn than Contract Bridge, and more congenial in the family circle than Poker.

But perhaps what really helped it on its way was its popularity with actors, stars and the celebrity-seeking riff-raff of Broadway and Hollywood, and the consequent publicity the game attracted to itself. Hardly a film of that period fails to mention it somewhere, or at least get it on screen. Even Flora Robson as Elizabeth I and Errol Flynn as the Earl of Essex appear to be playing it – though, unfortunately, not mentioning it – in The Sea Hawk (1940).

Joan Crawford was a great fan of gin rummy.

Two play, using a 52-card deck; each player is dealt 10 cards facedown, one at a time, beginning with the nondealer. The remainder of the deck, placed facedown, forms the stock, the top card of which is turned up beside it to start the discard pile. The nondealer may take the top card from the discard pile or refuse it; if the nondealer refuses, the dealer has the same option. If both refuse, the nondealer draws the top card of the stock. Thereafter, each player in turn takes the top card of either the discard pile or the stock and then discards one card faceup on the discard pile.

The object of play is to form melds as in rummy—either sequences of three or more cards of the same suit or sets of three or more cards of the same rank. After drawing, a player whose unmatched cards (less one discard) total 10 points or less may “knock” (by physically rapping the playing surface or by making a verbal declaration). Face cards count 10 points each, aces 1 point each, and other cards their index value. Upon knocking, a player melds up to 10 cards, with unmatched cards to one side, and then discards the 11th card. Melding all 10 cards is called going “gin.”

The opponent of the knocker may lay off unmatched cards upon the knocker’s sets, thereby reducing the opponent’s count. If the knocker has the lower count of unmatched cards, he wins the difference. Should the opponent have an equal or lesser count, he has undercut the knocker and receives the difference (if any) plus a bonus of 25 points. The knocker cannot be undercut if he has gone gin; he receives, in addition to the total points of his opponent’s unmatched cards, a bonus of 25 points.

The first to reach 100 points wins the game and receives a 100-point bonus. Each player then adds to his score 25 points for each hand he has won, called a box. If the loser has failed to score, the game is a shutout, or a schneider, and the winner’s total score is doubled. Gin rummy is frequently played with several variations and as a gambling game, often for a small amount of money per point.

Ref: casinodailynews, encylopeadia.com, parlettgames.uk