Wilson 2NT (Part of Wilson Raises) is based on three primary ideas:
Jacoby 2NT does not work well enough for the tournament player. It must be improved! When opener rebids four of his/her major, responder could easily have a strong hand and no space to ask. Wilson 2NT fixes this problem.
MLTC (Modified Losing Trick Count) is a much better hand evaluation technique for hands that have found good trump fits.
The Splinter bid is not used effectively or understood well by most players and it is an incredibly valuable conventional treatment.
There are three hand types that start with Wilson 2NT (over a 1♥ or 1♠ opening)
All limit raises with four-card or longer support for the Major (not including Splinters).
All game forcing raises with four-card or longer support for the Major (not including Splinters).
All Splinter bids with 5 ½ or fewer losers (MLTC). These hands are immediately in the slam zone and are too STRONG to be showed with an immediate Splinter bid.
The responses to Wilson 2NT are:
3♣ any minimum hand - A minimum hand can be up to a bad (5332) 14HCP. It may not hold fewer than 7 losers if balanced. Balanced = no singletons or voids; NOT FG; If unbalanced, it may not hold fewer than 6 losers.
3♦ balanced hand with extras, includes 5(422) shape; FG
3♥ extras, exactly five-card major, some shortness EITHER singleton OR void;
FG
3♠ extras, six+ card major; singleton; FG
3NT extras, six+card major; void; FG
4♣ extras, five+ clubs at least KQxxx; FG
4♦ extras, five+ diamonds at least KQxxx; FG
4♥ extras, five+ in other Major suit at least KQxxx; FG
Extras are defined as 15+HCP or fewer than six losers (MLTC)
Over the 3♣ response:
3♦ = asks again and is FG:
3♥ = depends on what trump are; if hearts are opened 3♥ shows a limit raise and is non-forcing. If spades were opened, 3♥ shows a very strong Splinter, 5 ½ or fewer losers
3♠ = depends on what trump are; if spades are opened 3♠ shows a limit raise and is non-forcing. If hearts were opened, 3♠ shows a very strong Splinter, 5 ½ or fewer losers
3NT = Very strong Splinter in clubs; 5 ½ or fewer losers
4♣ = Very strong Splinter in diamonds; 5 ½ or fewer losers
4♦ = not defined
4♥ = to play
4♠ = to play
4NT = RKB for whichever suit was opened
The continuations after 1M p 2NT p 3♣ p ?
3♦ = asks again and is FG:
3♥ = some shortness EITHER singleton OR void
3♠ = asks VLMH (Void, Low, Middle High)
3NT = Void!
4♣ = asks LMH (Low, Middle High)
4♦ = club void
4♥ = diamond void
4♠ = void in Other Major
4♣ = club singleton (Low)
4♦ = diamond singleton (Middle)
4♥ = Other Major singleton High)
3♠ = 5(422) with a quality 2nd suit (QJxx or better)
3NT = asks 2nd suit LMH
4♣ = 2nd suit is clubs
4♦ = 2nd suit is diamonds
4♥ = 2nd suit is hearts
3NT = 5(332) or 5(422) with a poor second suit (Q10xx or worse)
4♣ = six+ card suit; no shortness; ♣ Control
4♦ = six+ card suit; no shortness; ♦ Control; NO ♣ Control
4♥ = six+ card suit; no shortness; ♥ Control; NO ♦Control; NO Control
4♠ = MAY BE USED ONLY IF SPADES ARE TRUMP: six+ card suit; no
shortness; ♠ control; NO ♥ Control; NO ♦Control; NO ♣ Control
(Ex: ♠AKJxxx ♥xx ♦Qxx ♣Qx)
3♥ = Limit Raise NF if ♥ are trump: or a Splinter bid with 5 ½ or fewer loser if ♠
are trump
3♠ = Limit Raise NF if ♠ are trump: or a Splinter bid with 5 ½ or fewer loser if ♥
are trump
3NT = ♣ Splinter; 5 ½ or fewer losers
4♣ = ♦ Splinter; 5 ½ or fewer losers
After these bids, Control Showing Bids are on. If a void has been shown, you may use 4NT as RKB but you will not show the void again, nor is the Ace of the void suit counted as a keycard if opener bids RKC after showing a void.
After a 3♦response from opener (showing a balanced hand with extra HCP)
3♥ = asks
3♠ = 5(422) with a quality 2nd suit (QJxx or better)
3NT = asks 2nd suit LMH
4♣ = 2nd suit is clubs
4♦ = 2nd suit is diamonds
4♥ = 2nd suit is hearts
3NT = 5(332) or 5(422) with a poor second suit (Q10xx or worse)
4♣ = six+ card suit; no shortness; ♣ Control
4♦ = six+ card suit; no shortness; ♦ Control; NO ♣ Control
4♥ = six+ card suit; no shortness; ♥ Control; NO ♦Control; NO ♣ Control
4♠ = MAY BE USED ONLY IF SPADES ARE TRUMP: six+ card suit; no
shortness; ♠ control; NO ♥ Control; NO ♦Control; NO ♣ Control
(Ex: ♠AKQxxxx ♥Qx ♦Qx ♣Qx)
3♠ = Balanced Limit Raise; FG
3NT = ♣ Splinter; 5 ½ or fewer losers
4♣ = ♦ Splinter; 5 ½ or fewer losers
4♦ = Splinter in Other Major; 5 ½ or fewer losers
After these bids, Control Showing Bids are on. If a void has been shown, you may use 4NT as RKB but you will not show the void again, nor is the Ace of the void suit counted as a keycard if opener bids RKC after showing a void.
After a 3♥ response from opener (showing extras with exactly a five card suit and a singleton or void)
3♠ = asks for shortness (VLMH)
3NT = void somewhere
4♣ = asks where ( LMH)
4♦ = Low void; void in clubs
4♥ = Middle void; void in diamonds
4♠ = High void; void in other major
4♦ = asks where (HML)
4♥ High void; void in other major
4♠ Middle void; void in diamonds
4NT Low void; void in clubs RESPOND KEYCARD
4♣ = club singleton (Low)
4♦ = diamond singleton (Middle)
4♥ = Other Major singleton High)
3NT = balanced limit raise
4♣ = ♣ Splinter; 5 ½ or fewer losers
4♦ = ♦ Splinter; 5 ½ or fewer losers
4♥ = Splinter in Other Major; 5 ½ or fewer losers
4♠ = Balanced Limit Raise; FG After
3♠ = response (showing extra values, a six+ card suit, and a singleton)
3NT = asks singleton LMH
4♣ = singleton ♣
4♦ = singleton ♦
4♥ = singleton in Other Major
After these bids, Control Showing Bids are on.
After 3NT response (showing extra values, a six+ card suit, and a void)
4♣ = asks Void LMH
4♦ = void in ♣
4♥ = void in ♦
4♠ = void in Other Major
After these bids, Control Showing Bids are on. If a void has been shown, you may use 4NT as RKB but you will not show the void again, nor is the Ace of the void suit counted as a keycard if opener bids RKC after showing a void.
SOURCE: Kevin Wilson, http://bridgewinners.com/profile/kevin-wilson/