Jacoby transfer
The Jacoby transfer, or simply transfers, in the card game contract bridge, is a convention in most bridge bidding systems initiated by responder following partner's notrump opening bid that forces opener to rebid in the just above that bid by responder. For example, a response in diamonds forces a rebid in hearts and a response in hearts forces a rebid in spades. Transfers are used to show a weak hand with a long major suit, and to ensure that opener the hand if the final contract is in the suit transferred to, preventing the opponents from seeing  the cards of the stronger hand. The use of the 2 and 2 (and often 2) responses to an opening 1NT bid as transfers is one of the most widely employed conventions in the game. Less commonly, partnerships may agree to use transfer-style bids in a variety of other situations. History and purpose. First described in a series of articles by Olle Willner of Sweden in "Bridge Tidningen" in the early 1950s, transfers were popularized for English speakers in 1956 in "The Bridge World" article by Oswald Jacoby and have gained widespread international acceptance by duplicate and rubber bridge  players alike. In the article, Jacoby gave his name to the convention as the Jacoby Transfer Bid (JTB) stating that it was an adaptation of a bid then known variously as either the 'Texas Convention' or the 'Carter Transfer' (now known as the Texas transfer). The initial purpose of the convention was to make the notrump opener the declarer in a suit contract when his partner held a relatively weak hand with a long suit; this would make the opening lead come up to the stronger hand and such a situation is advantageous should declarer possess one or more or  tenuously guarded honors. In addition, the exchange of information by the transfer bid and subsequent rebids by responder and notrump opener "is designed to help partnerships reach the right contract", i.e. their optimum contract. In the 1990s further developments of the transfer procedures enabled them to be used to even greater effect. The use of "bouncing" and "breaking" rebids by opener offered partnerships the opportunity to find safe game and slam contracts with fewer high card points than with traditional methods. Initial transfer bid. The transfer procedure is quite simple and is described first in response to your partner's  1NT opening bid. Since a 1NT opening bid requires a balanced hand, i.e. no more than one doubleton, it promises to have at least two cards in the desired suit: Opener can super-accept the transfer by bidding three of the major with a maximum hand containing at least four cards in that major. An immediate disadvantage of this method is that it is incompatible with a weak take out into 2, although as with the loss of the 2 weak take-out when using Stayman, this is not generally considered a serious loss. Subsequent standard bids. After the transfer  has been completed by the 1NT opener, subsequent bids by the transfer initiator are: Non-standard but common subsequent bids. Since a 2 response is no longer required for a weak take-out into spades, it is often used in other ways: Modern additions to transfer procedures. Although part of the early writings on transfers in the 1950s, "bouncing" and "breaking" have only become widespread in the UK since the 1990s. As promulgated by Paul Mendelson, they are: With these two devices (bouncing and breaking) it is possible to discover, at very little risk, games that would otherwise be missed . Using transfers in other NT situations. Transfers work well following other notrump bids. A common usage follows an opening bid of 2NT where a weak take-out into three of a major becomes a possibility whereas with traditional methods such a bid would be forcing. Transfers following a double. Following a double (i.e. partner opens 1NT and intervening opponent doubles), there are two options in fairly common use: (Note: some partnerships use a "forcing pass" by the partner of the 1NT opener. The 1NT opener is then obliged to redouble. The partner of the 1NT opener may then pass the  redouble with a good hand and 1NT redoubled is judged to be makeable, or with a poor hand initiate bidding 4-card suits up-the-line until at least at 4-3 suit fit is found). Transfers following an intervening bid. Standard bidding in most systems is that all responses following a natural suit overcall are themselves natural bids ("double" may be used for take-out). An alternative is that such responses, including "double", act as transfers. For example, following a 1NT opening and a 2 overcall: