In bridge bidding, a bid of double can be played any time that an opponent made the most recent non-pass bid and that bid was a suit or notrump bid. If the final bid for the contract is doubled, then the below the line points for making the contract are doubled, and other scoring in the hand is also increased, but not necessarily exactly double.

In most conventions, a double of a low-level bid is usually for takeout, meaning that the doubler's partner is expected to take out the double by making a bid. If the next player passes, partner is required to make a bid, generally his best suit at the lowest level, and promises no particular strength in the hand. (If the next player bids, then the bid by partner is optional, since the double has already been taken out, and partner should only bid if he has a reasonable responding hand.)

If partner bids and the doubler then bids a different suit, this is called a double and bid. This sort of bid is used to show a strong hand with 17 or more high card points when the opponents open the bidding.