Developed by Oswald Jacoby, Jacoby 2NT is a bridge convention in which a bid of two notrump (2NT) over partner's opening bid of one heart (1♥) or one spade (1♠) shows a hand with both
This response is considered to be forcing to game in the suit of the opening bid. If the partnership plays splinter bids, the Jacoby 2NT response also denies a splinter (either no singleton or void, or stronger than the agreed range for a splinter bid).
With a balanced hand, opener rebids as follows:
With an unbalanced hand, there are two common methods of continuing rebidding over a Jacoby 2NT response, the choice of which is a matter of agreement between the partners. These methods differ only in the definition of a bid of another suit.
The earlier method uses the following bids.
The newer method uses the following bids.
The Jacoby 2NT bidder must assess how the hands fit, and generally will have the following options.
The 2NT bid is used in some systems to show an invitational or better raise (10 point upwards, at least four-card support, forcing to the three level only) rather than a game force. In 2/1 game forcing and Acol, this is used if opponents double and is called the Jordan 2NT convention in the USA; in the UK, it is sometimes called Truscott. Some books and articles, particularly in the UK, call this Jacoby 2NT, but this is technically incorrect.
The Jacoby 2NT was designed for five-card majors. It can also be used in a four-card major system such as Acol, but it may then be useful to change opener's rebids to allow him to specifically show a hand with only a four-card major, typically by using 3NT. Also, the three and four-level new suit rebids may be swapped so that a three-level bid shows a long suit and a four-level bid a shortage (splinter bid).
In some forms of Acol, a 3NT response is used instead of 2NT to show a hand with 13-15 points, four-card support and no side suit shortage (a "pudding raise").