Multi 2 diamonds

Multi 2 diamonds, or simply Multi, is a contract bridge convention whereby the opening bid of 2♦ shows multiple types of hands, which always includes a weak-two bid in either major suit, while the additional meaning may be a strong balanced hand (commonly 20-21 high card points), or a 20-22 three suiter. The inherent ambiguity as to both suit and strength makes it a powerful and popular convention capable of seriously disrupting the opponents' bidding.

Although it's technically a brown sticker convention (since no long suit is initially known), its popularity and availability of defenses persuaded World Bridge Federation to allow its usage on tournaments of lesser ratings. It is described in WBF Convention Booklet.

An opening bid of 2♦ classically shows one of four types :

Often the convention is played with only one of the strong options being present, i.e. a three-way bid. As long as at least one strong option is present, the multi 2♦ opening is a forcing bid. More recently a trend has been seen to play a "hearts only multi" in which the weak 2 option is always hearts. "Spades only multi" also presumably exists. The first response assumes that opener has a weak two in a major.

Another popular innovation is the 'mini multi', which contains no strong option. This variant is actually less legal (i.e. legal in fewer tournaments) than the traditional multi. This may seem odd, but there is a logical explanation. The reason is that the ambiguity inherent in a multi opening is a double edged sword - it can cause more problems for the pair using it than for their opponents (typically when the multi opener has a strong hand and his partner has support for both majors). This risk is no longer present when using the mini multi.

Responding to the multi:

Assuming his left hand opponent passes, the partner of the multi opener is forced to bid. He has several options available:

Action by responder if RH opponent doubles: 2♦ - X - ?

Opener's rebids:

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