2/1 game forcing (two-over-one game-forcing) is a style of bidding in contract bridge, and is the standard style of bidding for American duplicate bridge, having surpassed Standard American. It differs from Standard American in that a full opening bid is required for a response at the two level to an opening bid of one of a major.
In that case, the contract should usually reach game.
The 2/1 auctions are 1H-2C, 1H-2D, 1S-2C, 1S-2D, and 1S-2H. Hands without an opening bid are required to respond 1N to 1H or 1S. In Standard American, 1H-1N and 1S-1N are nonforcing, but in 2/1 game forcing, 1H-1N and 1S-1N is forcing for one round. Since this bid is forcing, hands with a three-card limit raise can start with 1N and later jump-support partner.
Most pairs don't play that 1D-2C is game forcing. Also, 2/1 game forcing doesn't apply to a passed hand. Some pairs play that 2/1 isn't absolutetly game forcing; you can stop below game only when responder rebids his suit. For example, 1H-2C-2H-3C is nonforcing by some 2/1 players. A regular partnership should discuss this possibility.
