42 is essentially a card game played with a standard set of 28 "Double-Six" Dominoes. Four players in two partnerships each receive 7 dominoes. The bid goes around once, with bids ranging from 30 to 42, plus some special bids. The winning bidder gets to declare a trump. From there it is like any trick taking game with the twist that the higher end of the domino led determines the suit for that round. Scoring for a round is one point per trick plus the "count". The dominoes that add up to 5 (0-5, 1-4, 2-3) or 10 (6-4, 5-5) are worth 5 or ten points respectively, giving a total maximum score of 42, and the name of the game.

A match is seven hands, or marks. Traditionally, scoring is the seven marks required to write the letters ALL.