Responding to Partner's Notrump Opening Bid

Simple arithmetic will almost always tell you how high you should place the contract when your partner opens 1NT. If partner opens 1NT (15-17 points) and you hold:

0-7 points -- Pass or play in 2 of your long suit (5+ cards).
8-9 points -- Invite game in notrump or your suit.
10-17 points -- Bid a game in notrump or a suit.
18+ points -- Bid a slam in notrump or a suit if you have an 8-card fit.

When deciding on your response, a hand with a long suits should be valued "up":

Add 1 point to your high-card total if you hold a good suit of 5+ cards.

Add in your distribution points if you hold a 6+-card major.

Standard American Responses to 1NT

2C = Stayman, asking partner to bid a 4-card major if he has one (see below).
Bid 2C with: ♠QJ32 K5 ♦K763 ♣943

2D, 2H or 2S = Signoff, showing a 5+-card suit and 0-7 points. It tells partner that you think 2 of a trump suit is safer than 1NT. Partner must pass.
Bid 2S with: ♠QJ854 ♥87 ♦J8 ♣9843
OR you can use the popular (and recommended) Jacoby transfer convention to describe any responding hand that has 5+ cards in a major suit.

2NT = Invitational, showing 8-9 points and no major. It invites partner to 3NT.
Bid 2NT with: ♠Q62 ♥K63 ♦102 ♣A974

3C or 3D = Forcing, with a long suit (5+ cards) and at least game values (9-10+ points). Unless your hand is very distributional or very strong (one with which you want to invite slam in your suit), bid 3NT instead of 3 of your suit.
Bid 3D with: ♠7 ♥K64 ♦AQJ954 ♣A102
But bid 3NT with: ♠7 ♥Q93 ♦AQJ954 ♣1032

3H or 3S = Forcing, with a 5-card suit and game values (9-10+ points). This forces partner to bid again. With a 5-card major and 9+ points, always jump to 3 of your suit to ask partner if he has 3-card support. If partner rebids 3NT, he has only 2 of your suit, so you should pass. If he raises your suit to 4, he guarantees 3+-card support.
Bid 3H with: ♠A6 ♥KJ1032 ♦9832 ♣J4
If you play Jacoby transfers, you'll transfer to your suit (by bidding 2D, which forces opener to bid 2H). Your next bid will be 2NT or 3NT to show your point-count and ask partner to choose between notrump and your suit.

3NT = 10-15 points and no possible major suit fit. Partner will always pass.
Jump to 3NT with: ♠A42 ♥J8 ♦7632 ♣KQ104

4C = Gerber convention, asking for aces. You can use this bid when you're sure of a slam in notrump or your suit and want to check to be sure you are not missing two aces.

4H or 4S = 6+-card suit and game values (8-9 or more points). Partner will always pass.
Jump to 4S with: ♠Q109865 ♥2 ♦AQ6 ♣1093
If you play Jacoby transfers, you'll transfer to your suit first (bid 2H to force opener to bid 2S), then raise to game in your major.

4NT = Invitational to 6NT, showing about 16-17 points. Opener will bid 6NT if he's on the "top" of his 15-17 points He can pass if he has a minimum.
Bid 4NT to invite slam: ♠J104 ♥AQ5 ♦AK ♣Q10932

The Stayman Convention -- 2C to ask for a major

This convention allows you to find the important 4-4 major suit fit after your partner opens 1NT. To use this bid, responder must have:

At least 8 points AND

At least one 4-card major suit.

With these hands, always bid 2C to ask the 1NT opener if he has a 4-card major. Opener will reply by bidding a major suit if he has 4-card length in it (if he has two 4-card majors, he'll bid 2H, the cheaper suit, to keep the auction low). If opener does not have a 4-card major, he'll bid 2D.

If the 1NT opener bids your 4-card major:

Raise to 4 of that suit if you have game values (at least 10 points).
Raise to 3 of that suit if you have invitational values (8-9 points).

If the 1NT opener bids a major you don't have (the auction goes 1NT - 2C - 2H, and you hold 4 spades):

Make your natural notrump bid -- 3NT if you have at least 10 points; 2NT if you have 8-9 points.
If you have the invitational hand with a 5-card major, bid 2 of your suit (see below).
With any point range, do not bid the other 4-card major. The auction has told partner that you have at least one 4-card major, so there's no reason for you to show it twice. If you don't raise the major that partner bid, he'll know you have the other one, and if he has 4 cards in that major, he'll show it with his next bid.

If the 1NT opener bids 2D (denying a major):

Make your natural notrump bid as above. You now know that partner doesn't have a fit with you, so don't bid your 4-card major.
If you have the invitational hand with a 5-card major, bid 2 of your suit (see below).

Another use of Stayman:

If you don't play Jacoby transfers, Stayman can also be used to start the description of an invitational hand (7-8 points) with a 5-card major -- a hand such as ♠K8762 ♥74 ♦A63 ♣J104

To show this type of hand, you start with 2C Stayman. If partner bids 2S (showing a 4-card suit), you've found a 9-card trump fit, and you should raise directly to 4S. If partner answers Stayman with 2D or 2H, you'll bid 2S to show a "real" suit and invite game.