A (bridge) signal is a move in the card game of contract bridge in which partners defending against a contract play particular cards in a manner which gives a coded meaning or signal to guide their subsequent card play. This may also be referred to as carding. Signals are usually given with the cards from the two-spot to the nine-spot. There are three types of signals:

The methods used for each type of signal have evolved over time and fall into two broad categories:

Partnerships decide on which methods to adopt and must disclose them to their opponents. Use and interpretation is dependent upon their context, such as the contract, the auction, the opening lead or prior play, the cards visible in dummy, the cards visible in one's hand, who has led to the current trick and whether following suit or discarding.

Accordingly, partnerships generally have an order of precedence for the interpretation of signals such as that indicated in the adjacent table. In the vast majority of cases, the third-hand follow-suit signal is an attitude signal, but when the attitude signal does not apply, it is a count signal. Usually, it is relatively easy to recognize a signal correctly when the declarer leads – either a count signal when following suit, or an attitude signal when discarding, and when they do not apply, it is a suit-preference signal.

While signals are a means of permissible communication between defenders, they are considered as providing guiding information to partner and are not absolutely binding; the partner may proceed otherwise as they deem rationally appropriate. Because the declarer is entitled to know the meaning of all partnership agreements, including defenders' signals, they are also privy to the information being exchanged; this may give way to falsecarding tactics by the defenders.

When signaling standard attitude, a high card is encouraging and a low card is discouraging. Attitude is normally signaled when following suit to partner's led suit and when discarding on either partner's or declarer's led suit.

For example, if one's partner leads with the Ace of Spades, one might signal with the nine if the King is held (requesting partner to continue the suit), or with the three if one holds nothing but spade cards with low ranks (notifying the partner that a switch to another suit is likely best).

One can only signal with the cards held. Signaling low is easy, but if one's lowest card is the eight, one's partner might have difficulty "reading" it as low. When signaling high, play the highest card possible. Having easily readable cards to signal relies on luck.