The Reverse by Opener

Basic bridge bidding is based on a practice called "up-the-line", which means that after you open, partner's one-level responses and your rebids are always made in the cheapest of your 4-card suits. For example, if you open 1C and partner has two 4-card majors, he'll always bid 1H to keep the bidding low and give you room to show a possible 4-card spade suit. This assures that you'll find any major-suit fit, and that you'll keep the bidding low until you've exchanged complete information about your suit lengths. (See the lesson on "Which Suit to Respond?" .)
If partner bypasses a suit he could have shown at the one-level, you should always assume (at least temporarily) that he does not have 4-card length in that suit. For example:
     You open 1D with  94  KQ103  AJ764  K10 and partner responds 1S. With your minimum opening, it's pointless to bid 2H (a suit partner has denied), which could force the bidding to the 3-level. You should rebid 1NT with this hand to show your minimum point-count and keep the auction low. It's possible that partner has 5 spades and 4 hearts, but in that case, he'll bid 2H over your 1NT rebid.
When you have a stronger hand, though -- such as  4  KQ103  AKJ76  A102 -- you can afford to take the bidding higher. To show extra strength, you can make a reverse, which is a bid of a suit partner has bypassed (in the above example, your rebid of 2H would be a reverse). Put another way, it's a bid that will force partner to bid at the 3-level if he prefers your first suit. Some typical reverse auctions are:
Opener Responder      Opener Responder      Opener Responder
1C       1H               1H       1NT               1S       2D
2D                        2S                         3C
A two-level reverse (where you must go to the 2-level to show your second suit) shows a distributional hand with extra strength, and it forces partner to bid again. Specifically, it promises: 1 - At least 16-17+ high-card pts.; 2 - At least 5-4 distribution in your two suits; 3 - Your first suit must be longer than your second suit; 4 - Your second suit must be higher in rank than your first suit; and 5 - Partner must have bypassed your second suit with his response. Opener's one-level rebid (1C-1H-1S) is not a reverse. Your rebid is a reverse only if you must go to a higher level to show the suit (1C-1NT-2S).
A three-level reverse is made when partner's response forces you to the 3-level to show your second suit. Like a two-level reverse, this is forcing and shows extra values. The only differences are that your second suit will usually be
lower in rank than your first suit, and you may have equal length in your two suits.
Here are some typical hands:
J107  3  AQJ7  AKQ102 -- You open 1C and partner responds 1S. You can now reverse with a rebid of 2D. This forces partner to bid again and give you more information. If he rebids a long spade suit, you'll raise to 4S. If he bids anything else, you can further describe your hand by bidding spades next. Note that since you didn't raise spades right away, you denied holding 4-card support. Your belated raise shows 3-card spade support and , by inference, tells partner you have a singleton heart (since you've shown 9 cards in clubs and diamonds and 3 cards in spades).
AQJ106  J  KQ1076  A5 -- You open 1S and partner bids 2H, showing 10+ pts. and at least 5 hearts. Since you must go to the next highest level to show your diamond suit, a 3D bid here is a 3-level reverse (often called a high-level reverse). With a weaker hand (12-14 pts.), you would rebid 2S to show a minimum and keep the bidding low.
AK1054  KQ9862  A4  Void -- You can also use a reverse bid when your suits are longer than 5-4. Here, you open 1H, partner responds 1NT, and you make a reverse bid of 2S to force. Over whatever partner bids, you'll bid your spades again to show extra length. Partner will know that you must hold 5 spades (because you bid them twice) and 6 hearts (because your hearts must be longer than your spades). Partner can now decide what the trump suit should be.
K9  AQ72  AQ  KJ754 -- You open 1C and partner bids 1S. This hand qualifies as a reverse to 2H, but a 2NT rebid is a better description of your strength and distribution. Your hand is fairly balanced, your suits are not robust, and you have almost half your points in your doubletons. If you instead bid 2H here, you promise only about 17+ pts., and you tend to show a hand that's more suitable for a trump contract than for 3NT.
Responding to a reverse

Opener's reverse is forcing for one round -- you must bid again, even if you have a very weak response. In general, you should base your rebid on your picture of partner's hand (he's shown at least 5-4 in his suits) and try to support one of his suits if possible. Here are some simple meanings for your second bid, in the general order of preference you should consider them:

Raise of partner's second suit (1C-1S-2H-3H) = 4-card support

Bid of partner's first suit (1C-1S-2H-3C) = 3+-card support

Jump in partner's first suit (1C-1S-2H-4C) = a strong, distributional hand with 4-5 cards in partner's suit and slam values (12+ playing pts.)

Rebid of your own long suit (1C-1S-2H-2S) = very weak hand (5-7 pts.) with 5+ (preferably 6) cards in your suit and no fit for partner's suits.

2NT = weak response (5-7 pts.) with a stopper in the unbid suit. You can also choose to use 2NT here as the Lebensohl 2NT Convention (see below).

3NT = good values (8-11 pts.) with stoppers in the unbid suit.

The unbid suit (1C-1S-2H-3D) = forcing and could be artificial, usually without support for partner's suits. Like "New Minor Forcing", a bid of the fourth suit can be used when you have a good hand (8+ pts.) and want to find out if opener has 3-card support for your major.

If you'd like a more accurate way to rebid after a reverse, you can use a popular convention called the Lebensohl 2NT. See the lesson on Lebensohl over Reverses on this site.
　

　