Opening in NT
With a flat hand and 12 to 14 points, open 1NT.
With 20 to 22 points the bid is 2NT.
A strong unbalanced hand is better bid as 2C.
Having opened NTs the opener must not bid again unless invited.
Responding to 1NT
With 20 points or more the responder can go straight to a slam.
With a balanced hand and 18 points the responder bids 4NT (quantitative bid) which asks the opener for the strength of her hand. If opener has 14 points she rebids 6NT, if fewer she passes.
With 11 points balanced or a minor, the responder bids 2S. With 14 points the openers bids 3C, with fewer bids 2NT. The responder can then correct to the preferred minor.
With 12 points the responder bids 2NT. The opener raises to 3NT with 13 or more.
With 10 points or fewer and a balanced hand, the responder should pass.
If a responder has at least five cards in a major and is weak (less than 7 points) OR strong (opening hand or better) then a red suit transfer is used to allow the opener to rebid the major.
If the opener has 4 cards in the transferred suit she jump bids the transfer. This is called a super transfer. The responder can then decide whether a game contract is possible.
By rebidding the major at three level the responder invites the opener to chose between game in the major or in no trumps.
If the responder has clear reasons not to want to play in no trumps then she rebids to game level in her major suit.
There are times when the responder wants to be a game contract but does not want her hand exposed as dummy. In this case the response in a major suit is to go straight to game.
With a weak hand and a long minor the responder may wish transfer to a minor by bidding 3C or 3D.
The opener must not bid again.
Before using this bid remember that it requires you to win 9 tricks so have a very good reason not to be in NT.
If the responder has a long minor suit and an opening hand ,a transfer or a 5 level contract in a minor suit should not be considered. No trumps is nearly always preferable because it scores more points and needs fewer tricks.
The response of 2C is a convention used to determine the best contract for game. It should not be used with a weak hand.
The bid of 2C is a question asking for a four card major it is not a promise of the responder having both majors.
If the opener does not have a four card major she bids 2D.
After the opener's rebid the responder’s decision is final. A bid of 2NT means just that.
To overcall 1NT the overcaller has the following options -
With a strong hand (16 plus), double.
With an opening hand and a good quality five card suit, bid at the 2 level.
With a good quality 6 card suit and more than 8 points, bid at the 2 level.
Response to a double
Always remember that the opener in 1NT has at least 12 points. By adding her own hand to the opener, the responder knows the total strength of the partnership. If the total is less than 19 the contract is likely to fail, with a penalty score. If 20 or more, success is likely with a bonus score.
Therefore, the responder only needs to bid if the contract is destined to fail. This is called a weak takeout and is not an invitation for the opener to rebid even if she only has two cards in the takeout suit.
If the overcaller's partner bids after the weak takeout the opener must not bid.
The Moscow Defence can also be used if 1NT is doubled.