Weak Two-Bids

Weak Two-Bids are popular because they allow you to preempt more often (making it difficult for the opponents to bid when it's their hand) AND because they provide a good description of your hand (making it easier for your partner to bid when he has strength). To play Weak Two-Bids, you and your partner must agree to change the meaning of all four opening Two-Bids. The new meanings are:

2C = Artificial and forcing, showing a Strong Two in a suit (or notrump) to be named at your next bid. 2C forces the partnership to at least 3 of a major. To decide whether or not you should open a Strong 2C, you can use the same general guidelines you would follow for old-fashioned Strong Two-Bids.
2D, 2H, 2S = Good 6-card suit, 5-11 pts., no more than one Ace or King outside your suit. A Weak Two is a preempt, but tends to be more constructive than a 3-bid.

Watch the vulnerability!

If you're not vulnerable, you can open a Weak Two with very light hands:: K109654 43 753 K5 or 432 AQ9875 753 5

A vulnerable Weak Two should promise a stronger suit and more playing strength:: KQJ987 4 764 K54 or 73 4 AQJ1084 J1085 .

Responses to a Strong 2C Opening

2D = A "waiting" bid that lets the 2C opener describe his hand. You can bid 2D with a negative hand (0-7 pts.) or a better hand that has no clearcut action.
2H, 2S, 3C, 3D = Positive response (7+ pts.) & good 5+-card suit (AK, AQ or KQ).
2NT = 8-10 pts., balanced distribution.

After 2D (the most common response), opener will bid his long suit. You can then bid naturally (raise his suit with support or bid a 5+-card suit of your own).

If you have a "double negative" (0-3 pts. with no fit for partner), respond 2D, then bid the cheapest number of notrump over partner's rebid. You can then stop below game (3H, 3S, 4C or 4D) if partner doesn't have a super-strong hand.

Responses to a Weak-Two Opening (2D, 2H or 2S)

Partner's Weak Two is a preempt -- you're not obligated to respond unless you want to preempt higher in his suit or try for game. The meanings of responses are:

New suit = Strong hand, good 5+-card suit. The Weak Two opener must bid again.
2NT = Good hand (usually with a fit for partner's suit), at least invitational to game. 2NT asks opener to show an outside Ace or King by bidding that suit at the 3-level. If he doesn't have one, he "retreats" to 3 of his suit.
Simple raise of opener's suit = A weak, competitive raise. It shows a fit for partner's suit and a few tricks, but is not invitational to game-partner should always pass.
3NT or 4 of a major = To play. Partner should not bid again.

To assess your chances for game, don't count points. Since you have a picture of partner's hand, you should instead count winners and losers. For example:

QJ52 J KQ732 AQJ: If partner opens 2H, pass. Even though you have 16 pts., your poor fit gives you little hope of game. You have 4 possible losers in the outside suits and partner could have 2 heart losers. Even if partner has an outside Ace or King, you can't count 10 tricks. However, if partner had opened 2S, your trump fit makes this hand much more powerful, and you would bid 4S.

J854 6 KQ65 KQ73: If partner opens 2S, bid 2NT to ask for an outside Ace or King. If he answers 3C or 3D, bid 4S. Count your tricks: 3 in the minor where partner has the Ace, 1 in the other minor, 5-6 spades (your length fills in his suit) and 1 or more heart ruffs in dummy. If partner instead answers 3H, you aren't sure of game, so bid only 3S and let partner decide.