In the card game bridge

Contract bridge

Contract bridge, usually known simply as bridge, is a trick-taking card game using a standard deck of 52 playing cards played by four players in two competing partnerships with partners sitting opposite each other around a small table...

, a takeout double is any call of "double" that shows a desire to compete for the contract by further bidding. Many takeout doubles nearly require partner to bid; partner should pass for penalty with an appropriate hand, but that is uncommon. Double for takeout is a convention whereas a natural double suggests the most recent bid, doubled, as a final contract (penalty double).

Perhaps the oldest bidding convention and the most common takeout double is the a double in response to an opening bid of one of a suit. Dbl
Commonly this double shows a hand of nearly opening strength with support for all three unbid suits, but shortness in the suit doubled. It strongly asks partner to bid.
Commonly double is considered takeout whenever one of the following conditions is met (but see balancing double below):

• Opponent(s) have previously bid only one suit, and the player did not have chance to double that suit before.
• Opponents have previously bid two suits, and the partner has passed.
• Opponents have found a fit.

Requirements

Most common requirements to make a takeout double are:

• Shortness (doubleton or less, tripleton at most) in the opponents' suit(s),
• Length (at minimum 3 cards, preferably 4) in the unbid suits,
• High-card point strength of at least a minimal opening bid (11 HCP)

The most common treatment is that the fewer high card points the hand possesses, the more strict are the distribution requirements (i.e. opponent's suit(s) shorter and unbid suits longer). Most players play that hands with 16(17) high card points should double regardless of distribution (unless the hand is suitable for 1NT overcall

Overcall

In contract bridge, an overcall is a bid made after an opening bid has been made by an opponent; the term refers only to the first such bid. A direct overcall is a bid made directly over the opening bid by right-hand opponent; an overcall in the 'last seat' is referred to as a balancing...

). Also, more high-card strength is required when opponents have bid on higher levels (e.g. preempt

Preempt

Preempt is a bid in contract bridge whose primary objectives are to thwart opponents ability to bid to their best contract, with some safety, and to fully describe one's hand to one's partner in a single bid. A preemptive bid is usually made by jumping, i.e. skipping one or more bidding levels...

ed). Most players play that a double up to the level of 4 is takeout, while doubles on higher levels are for penalties or "cooperative" (i.e. the partner is supposed to pass unless his distribution and/or strength indicates that playing a contract of their own on a higher level is a better prospect).

Examples

1)	This card is a minimal takeout double when the opponent opens 1. With other opening bids, it should be passed though. Also, if the opening bid was 3, the hand would be not strong enough to double.
2)	If opponents have bid 1 – 1, the takeout double shows unbid suits (spades and clubs)
3)	With 16 balanced points, this card is suitable for 1NT overcall over any opening bid rather than for a double.
4)	With 17 points and excellent spade suit, this card should double RHO's opening bid rather than overcall spades. Whatever partner bids, a subsequent bid of spades will indicate a stronger hand than a simple overcall.
5)	Over an opening bid of 1 this hand can double or overcall 2 depending on style and agreements. However, over an opening bid of 1, it should pass, expecting to double later opponents' heart or notrump contract for penalties.

Responses

Normally, (assuming the RHO passes) the doubler's partner should make a descriptive bid indicating a long suit of his own and the high-card strength:

• A minimal-level bid of a suit indicates a weak hand (normally, below 9 high-card points).
• A jump-bid of a suit shows a long (at least a 4-card) suit and invites the partner to bid on if the double was not minimal. Normally, such bid is made with 9-11 points.
• A bid of 1NT shows 8-10 HCP and balanced hand with at least one stopper in the opponent's suit. A bid of 2NT shows 11-12 HCP and balanced hand with stopper(s). One conventional alternative (Bungay Black Dog Double) is that 1NT shows 6+ points and the cheapest bid in a suit is a natural "weak squeak" denying 6 points.
• With any hand of opening-bid strength or higher, the responder should cuebid opponent's suit. The doubler is supposed to make a descriptive bid
• Finally, the takeout double can be passed for penalties in extreme situations, when the hand has 5-6 or more excellent trumps (this is termed a "penalty pass" or "converting the double"). The doubler is supposed to lead a trump, so that the opponent's trumps can be drawn. For this reason, it's not recommended that a takeout double be made with a void in the suit doubled.

If the RHO bids, the doubler's partner is not forced to make a bid anymore; if one is made, it is a free bid, indicating a certain strength and/or length in the suit bid.

The strength requirements above are lowered when the partner is known to be stronger (e.g. an opponents' preempt is doubled), and raised when partner can be weak (as in protective position).

Later-round takeout doubles

Double can be for takeout even in later rounds of bidding. As before, it denotes support for unbid suits and, often, extra values. In general, any low-level double after opponents have bid a suit (especially if they have found a fit) and partner has passed is generally played for takeout:

• the opener himself can double for takeout in the second round of bidding, after the opponents have entered the auction and partner had (usually) passed
• also, an overcaller can second-round double as well, to show extra values and support for unbid suits.
• a first-round takeout doubler can make a takeout double again, with a strong hand (around 16+ points)

1) 1 – (1) – pass – pass; Dbl	This type of is referred to as "reopening double", and shows shortness in spades and support for other suits
2) 1 – 1 ; Dbl	Shows 4+ cards in all unbid major(s), or 4+ cards in each minor if both bid suits are majors. See negative double Negative double The negative double is a form of take-out double in bridge. It is made by the responder after his right-hand opponent overcalls on the first round of bidding, and is used to show both support for the unbid suits as well as some values. It is treated as forcing, but not unconditionally so... .
3) 1 – Dbl – pass – 1; Dbl	Again, the opener has shortness in spades and other three suits.
4) 1 – 1 – pass – (2); Dbl	This shows shortness in hearts, but the opener must have extra strength, as the responder is forced to bid on level 2 or 3.
5) (1) – 1 – (2) – pass; (pass) – Dbl	The overcaller shows shortness in diamonds, and at least 3 cards in hearts and clubs, with some extra values for the overcall.
6) (1) – Dbl – (2) – pass; (pass) – Dbl	The original doubler shows extra values and/or extreme shortness in hearts.

Protective and balancing doubles

Distribution and strength requirements for a takeout double are lowered in situations when opponents' previous auction indicates that the partner has high-card strength, but was likely unable to take an action of his own because his distribution was not suitable for a double or an overcall.

A protective double can be made with as little as 8 high card points if both the RHO and the partner have passed the opening bid. Such a situation indicates that partner has strength, but was unable to act, perhaps because he had a hand like 1) or 5) in the table above:

West	North	East	South
1	Pass	Pass	?

South, holding can now double, expecting to find partner with strength and likely length in hearts, allowing him to pass for penalties or make a bid.

A balancing double occurs in later rounds of bidding, in situations where opponents have found a fit, but stopped on a low level, placing some points with the partner. It is normally done with a relatively weak hand and the distribution need not be perfect.

West	North	East	South
1	Pass	1	Pass
2	Pass	Pass	?

South, holding was not strong enough to double in the first round. However, he can expect the partner to have shortness in hearts and likely 4 cards in spades or diamonds, and thus make a balancing takeout double. Such doubles are more frequent on matchpoint scoring, where even a penalty of −100 for the failure to make 2 can be profitable against −110 or −140 that the opponents could score in 2.

Reopening double

Reopening double is a form of takeout double bid by the opener himself, after his left-hand opponent has overcalled and partner has passed. As normal takeout double, it shows support for unbid suits:

West	North	East	South
1	1	Pass	Pass
Dbl

West's double denotes shortness in spades, and invites partner to bid his best suit. A suitable hand would be e.g. . The partner should bid his longest suit on the lowest level with approximately 0-6 points, 1NT with 5-7 points and stopper in spades, (as he would bid 1NT immediately with 8-10 points), and jump in a suit with 7+ points. Finally, he can pass for penalties with 5 or more cards in spades.

Reopening doubles once showed extra values as well. With adoption of the negative double

Negative double

The negative double is a form of take-out double in bridge. It is made by the responder after his right-hand opponent overcalls on the first round of bidding, and is used to show both support for the unbid suits as well as some values. It is treated as forcing, but not unconditionally so...

, however (a takeout double by responder), responder must pass with length and strength in the opposing suit. In order to protect against such situations, opener is obliged to double even with thin values, whenever his distribution is suitable. Some pairs even require open to act somehow; responder's pass is forcing.