1NT Opening

General

The opening bid of 1NT promises 10-14 HCP balanced, 9-13 HCP unbalanced in a hand with no four-card major, six-card minor, or two five-card minors. Clearly the responding structure has no use for Stayman. Instead responder has available transfers two steps below the suit shown, and a 2H game forcing relay. This relay asks for further description of opener's hand in the normal manner. After subsequent bids by opener, responder continues to bid Step 1 for relay.
In third or fourth position, 12-16 HCP is required. The shape is expected to be classically balanced, with the proviso that any four-card major is either a weak suit or found in a 4333 pattern.

Responding to 1NT

2C Transfer to hearts showing 5+H.
2D Transfer to spades showing 5+S.
2H Game-forcing relay
2S Range-probe.
2NT Both minors, asking opener for preference. Usually responder will play at the three level.
3C Natural, not constructive showing 5+C.
3D Natural, not constructive showing 5+D.
3H Natural, forcing 6+H.
3S Natural, forcing 6+S.
3NT To play.
4C To play (mildly invitational).
4D To play (mildly invitational).
4H To play.
4S To play.

Responding to 1NT in 3rd or 4th seat

2C Garbage Stayman
2D Transfer to hearts showing 5+H.
2H Transfer to spades showing 5+S.
2S Both minors
2NT Invitational.
3C To play.
3D To play.
3H Natural, invitational 6+H.
3S Natural, invitational 6+S.
3NT To play.
4C To play (mildly invitational).
4D To play (mildly invitational).
4H To play.
4S To play.

Relay structures

After 1NT 2H

The off-shape possibilities require a relay structure different from those found elsewhere in the system.

2S 5D
2NT Game-forcing relay
3C 5D 4C
3D Game-forcing relay
3H 3=1=5=4
3S 2=2=5=4
3NT+ 1=3=5=4
3D 3=3=5=2
3H 3=2=5=3
3S+ 2=3=5=3
2NT Balanced no 5m
3C Game-forcing relay
3D 3=2=4=4
3H 2=3=4=4
3S 3=3=4=3
3NT+ 3=3=3=4
3C 5C 4D
3D Game-forcing relay
3H 3=1=4=5
3S 2=2=4=5
3NT+ 1=3=4=5
3D 3=3=2=5
3H 3=2=3=5
3S+ 2=3=3=5

After Transfers

Opener bids Step 1 with doubleton support and Step 2 with 3-card support. New suits by responder are natural and invitational. 2NT and 3NT are natural and non-forcing. Note that this structure permits responder to scramble out of 1NT with various atypical holdings. By transferring to spades, By transferring to hearts,

After 3H and 3S responses

Opener bids 3NT with 2M, cuebids with 3M and a suitable hand, and bids 4M with 3M and an unsuitable hand.

Competitive Bidding

When the opponents double our 1NT opening in the direct seat, we use two level bids by partner to show desire to play the contract named, or in the case of the 2C and 2D bids, desire to redouble that contract for rescue to higher-ranking strains. In effect these bids show at least five or fewer than three cards in the denomination named. We use a redouble to begin a scramble sequence with responder showing exactly 4C and another suit of at least four cards. We use pass to indicate any 4333 hand or any hand with values sufficient to play here doubled.
When the opponents double our 1NT opening in the passout seat, opener must pass and responder may pass for penalties, bid a suit to play or redouble to ask for a minor-suit preference to begin any scrambling auction.
After two-level interference we use penalty doubles. If the suit bid by the opponents is not or may not be a suit they hold then double shows interest in penalising at least one of the suits they might hold. If a specific minor suit has been shown by either side, 2NT is used in a Lebensohl sense. If no specific minor suit has been shown, then 2NT asks for minor-suit preference. After higher interference we use penalty doubles. Almost all undefined 2NT bids in competition show two places to play.
When the opponents compete after the game-forcing relay auction has begun, the agreements used are identical to those used after interference during other relay auctions.

Optional multi-transfer style

The double-under transfers to the majors become three-way: either Responder then reveals a three-suiter, makes an invitational major suit bid, shows a splinter, offers a choice of 3NT or a major suit game, or signs off in a major suit game.
The three-suited auctions achieve the effect of a stopper ask and splinter in the short suit and it is appropriate that the 1NT opener direct the auction opposite these hand types. Hereafter "three-suited" is understood to include 5-4-3-1 patterns and a three-card holding in such a pattern is deemed a suit. Such three-suited hands have an AKQ base of 7, and zoom base of 11.
4=1=4=4 and 1=4=4=4 bid their major suit immediately over 1NT and 4=0=4=5 and 0=4=5=4 bid their major suit after first bidding 2NT showing minors. All other three-suited hand shapes go via the transfers. Specifically, 2C is bid on all hands with both major suits, and 2C/2D is bid on all hands with 5C/D, or 0-1 S/H, or 3=5/5=3 in the majors (which is all of the rest of the three-suited hands).

After 1NT 2C/2D; 2D/2H/2S

In the structure below, after 1NT 2C; 2D/2H/2S, "M" refers to hearts and "m" refers to clubs, and after 1NT 2D; 2D/2H/2S, "M" refers to spades and "m" refers to diamonds. "OM" then refers to the other major and "om" to the other minor. "M*" refers to the major for which opener has shown fit with their first rebid and "OM*" refers to the other major. A shorthand like 4=1-3-5 means a pattern with 4S, 1H, and either 5D and 3C or 3D and 5C. As above, opener rebids Step 1 holding a doubleton M and rebids Step 2 with 3-card support. Responder's next bid follows the same scheme after either initial transfer (except that 2S is only available after an initial 2C, and in those auctions responder's final shape resolution will depend on opener's stated fit for the supposed initial transfer). After responder completes showing a three-suited shape, a natural slam interest auction continues.

2S Three-suited with both majors.
2NT Game-forcing relay
3C 0-1C, not 4=4=4=1 (note symmetric structure for 0-1D below)
3D Game-forcing relay
3H 5-4-3=1
3S Game-forcing relay
3NT 5OM* 4M* 3D 1C
4C 5M* 4OM* 3D 1C (bypassing 3NT only when there is a major-suit fit)
3S 4=4=5=0
3NT 5OM* 4M* 4D 0C
4C 5M* 4OM* 4D 0C (bypassing 3NT only when there is a major-suit fit)
3NT To play, C soundly stopped
3D 4=4-1-4
3H Game-forcing relay
3S 4=4=4=1
3NT 4=4=1=4
3H 5-4-1=3
3S Game-forcing relay
3NT 5OM* 4M* 1D 3C
4C 5M* 4OM* 1D 3C (bypassing 3NT only when there is a major-suit fit)
3S 4=4=0=5
3NT 5OM* 4M* 0D 4C
4C 5M* 4OM* 0D 4C (bypassing 3NT only when there is a major-suit fit)
2NT 5+m (431) remainder, GF
3C Game-forcing relay
3D 5+m 1H (43) remainder (note symmetric structure for 0-1S below)
3H Game-forcing relay
3S 4S 1H 5m 3om
3NT 3S 1H 5m 4om
3NT To play, H soundly stopped
3H 1om (43) in the majors
3S Game-forcing relay
3NT 4OM* 3M* 5m 1om
4C 4M* 3OM* 5m 1om (bypassing 3NT only when there is a known major-suit Moysian fit)
3NT To play, om soundly stopped
3S 1S 4H 5m 3om
3NT 1S 3H 5m 4om
3C short OM, GF, either 5M 1OM or 4om 0OM
3D Game-forcing relay
3H 5M 1OM (43) in the minors
3S Game-forcing relay
3NT 5M 1OM 4D 3C
4C 5M 1OM 3D 4C
3NT To play, OM soundly stopped
3S 5M 0OM 4D 4C
3NT 4M 0OM 5m 4om
3D 5M 3OM (41) in the minors
3H Game-forcing relay
3S 5M 3OM 4D 1C
3NT 5M 3OM 1D 4C
3M Invitational normally 6-card suit (might be 5 if fit has been shown)
3OM Unspecified splinter with M as trumps
Step 1 Game-forcing relay
Step 1 0-1C
Step 2 0-1D
Step 3 0-1OM
3NT 5M game values, opener is expected to bid 4M with support unless 3=3-3-4
4C Splinter with m as trumps, 0-1om
4D Splinter with m as trumps, 0-1H
4OM Splinter with m as trumps, 0-1S Note 2C is followed by 4S, unlike 2D followed by 4H
4M To play
In competition, responder is assumed to have a weak major-suit hand until responder's auction is most consistent with another hand type.