Named for its inventor, Oswald Jacoby

Oswald Jacoby

Oswald Jacoby was an American contract bridge player and author, considered one of the greatest bridge players of all time. He also excelled at, and wrote about, other games including backgammon, gin rummy, and poker.Born in Brooklyn, he was taught to play whist at the age of six and played his...

, Jacoby 2NT is a bridge convention in which a bid of 2NT over partner's opening bid of 1 or 1 shows a hand with both

• opening strength (nominally 13 HCP or "Rule of 20" depending upon partnership agreement) and
• support of at least four cards in the opening bidder's major suit.

This response is considered to be forcing to game in the suit of the opening bid. If the partnership plays splinter bid

Splinter bid

In contract bridge, a splinter bid is a convention whereby a jump bid in a side-suit indicates a trump fit and a singleton or void in the suit bid. For example, a 4 clubs response to a 1 heart opening establishes hearts as trump suit and indicates a singleton or void in clubs. Most experts agree...

s, the Jacoby 2NT response also denies a singleton or void.

Opener's Rebids Over a Jacoby 2NT Response

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.

Opener's Rebids Specific to First Method

The earlier method uses the following bids.

• With a void in spades or a singleton in any suit, the opening bidder cue bids three of the short suit.
• With a void in hearts, diamonds, or clubs, the opening bidder cue bids four of the void suit. (Note that the opening bidder must cue bid 3 rather than 4 with a void in the spade suit so a Jacoby 2NT responder who judges that slam is not in the cards can sign off at 4.)

Opener's Rebids Specific to Second Method

The newer method uses the following bids.

• With another good five card suit, the opener bids four of the second suit.
• With a singleton or void in the absence of another good five card suit, the opening bidder cue bids three of the short suit.

Opener's Rebids Common to Both Methods

In either method, with a balanced hand, opener rebids as follows:

• With 16 or more HCP opener rebids three of the agreed suit.
• With 14-15 HCP, the opener rebids 3NT.
• With fewer than 14 HCP bids four of the agreed suit.

Rebids by the Jacoby 2NT Responder

The Jacoby 2NT bidder must assess how the hands fit, and generally will have the following options.

• The Jacoby 2NT bidder may sign off in four of the opener's major (or pass, if the opener has already bid four of the opening major).
• The Jacoby 2NT may use cue bid
  Cue bid
  In contract bridge, a cue bid is a term that applies to two types of bid:*A bid of a suit that has already been bid by opponents.*A slam-investigating bid made during an auction's later rounds that shows control of a suit...
  
  s and/or slam conventions to find the best contract if the bidding suggests a possibility of a slam.