In the card game of bridge, the unusual notrump is a conventional bid showing two lower unbid suits.

When the right-hand opponent opens 1♥ or 1♠, the immediate overcall of 2 NT shows at least 5-5 in the minor suits (that is, at least five clubs plus at least five diamonds) and, presumably, a weakish hand (6 to 11 points). If the next player passes, the partner is expected to select the monor suit that he/she prefers and bid it at the 3-level.

The unusual notrump is used only after the opponents open the bidding. In addition to succinctly describing the hand to the partner, it also deprives the opponents of a lot of bidding space (that is, it has a preemptive value).

Many players extend the convention to have it show the "two lowest unbid" suits rather than strictly the minors. Thus, over 1♣, 2NT shows diamonds and hearts; and over 1♦, it shows clubs and hearts.

If the 2 notrump bidder bids again freely, then it shows a strong two suiter. To distinguish the weak and strong holdings, many partnerships agree not to use the unusual notrump for intermediate hands (about 12 to 14 points); they would simply overcall with one of their suits and show the other later if the bidding offers a chance. However, for two-suiters, many players apply losing trick count (LTC) instead of point count, as it more accurately depicts the offensive trick-taking potential of the hand. With LTC in effect, the required strength is about 4.5?7 losers, the latter only in favorable vulnerability.

Similarly, a 4NT overcall shows an extreme two suiter (usually at least 6-5, often 6-6 or 7-6) and enough trick-taking potential so that a 5-level contract can be made, or a sacrifice will likely be profitable. It shows the same two suits as 2NT would show. Note that 4NT is "unusual" only when the opponents open the bidding; when your side opens the bidding 4NT is normally played as the Blackwood convention or a quantitative invitation to 6NT.

The unusual notrump is one of the earliest conventions devised for the game. It extended the principle that when the natural meaning of a bid is not generally very useful, it is profitable to agree that it means something somewhat opposite. That is, while natural notrump bids show a strong hand with balanced distribution, the unusual notrump shows a weak hand with very unbalanced distribution.

The Michaels cuebid is a similar convention which is used to show a two suiter with one or both major suits.

To counteract the unusual notrump, the opening side may employ unusual vs. unusual.