Suction is a contract bridge bidding convention used to intervene over an opponent's 1NT opening.[1] Using the suction convention, a suit overcall of a 1NT opening is conventional and denies the suit actually bid. It shows either:
The overcall bids are summarized as follows:
| Opener | Overcaller | |
| Bid | Meaning | |
| 1NT | 2♣ | diamonds, or hearts and spades (i.e. both majors) |
| 2♦ | hearts, or spades and clubs (i.e. both black suits) | |
| 2♥ | spades, or clubs and diamonds (i.e. both minors) | |
| 2♠ | clubs, or diamonds and hearts (i.e. both red suits) | |
If responder passes, advancer is required to bid the next higher ranking suit. If overcaller has the one-suited hand, he passes. Otherwise, he bids yet the next higher suit, showing that suit plus the remaining, unbid suit. Advancer then takes a preference by passing or bidding the remaining suit.
Optionally additional overcalls are available to show the two non-touching suit pairs in the foregoing table – namely clubs with hearts and diamonds with spades. The first pair are referred to as the 'rounded' suits and the other as the 'pointed' suits owing to the shape of the tops of their pips. A call of 'Double' would show clubs and hearts (the rounded suits) and a call of 2NT would show diamonds and spades (the pointed suits). This requires the penalty double to be abandoned; if not abandoned, 2NT would show both non-touching pairs, requiring identification.