When an opponent opens the bidding, you can overcall in a suit or in notrump. When you overcall in a suit you
must have at least a five-card suit whether you are bidding a major or a minor suit. When you overall at the one
level you may have between 8-17 HCP. When you overcall at the two level, you show a hand that is strong
enough to have opened the bidding in first seat if no one else had bid, which means you pass the Rule of 20. To
overcall 1NT, you should have a balanced hand with 15-18 HCP and a stopper in the opponents’ suit.

1. To inform partner about a good, long suit.
2. To get your side into the auction
3. To suggest a specific lead to partner; and/or
4. To take away bidding space from the opposition

-Length - you must have 5 cards in the suit.  Whether you are bidding a minor or a major, you must have 5 cards in the suit when you overcall.  

-Points - the standard answer is that you must have 8-17 HCP, but the reality is that the analysis is more complex.  The number of points you need is a sliding scale depending on how good your suit is.  The better the suit that you are overcalling, the fewer points you need.  The worse your, suit the more points you need.  So, in deciding whether to overcall,, we need to evaluate how well it suggests a place to play, how well it suggests a lead, and how much room it takes up from the opponents.

Let’s look at 2 example hands:  

A) ♠AQJT9,♥32,♦432,♣432
B) ♠K,♥QJ,♦T8543,♣KJ32

Our RHO opponent opens 1♣.  Hand B has 10 HCP and Hand A has 7 HCP.  Which hand would you rather overcall?  
You would rather overcall Hand A by a wide margin.  Why?
- First, hand A suggests the only spot where we can reasonably expect to play any sort of contract.
- Second, hand A suggests a lead that we would want against all possible enemy contracts.
- Third, by bidding 1♠, we take the entire 1-level away from the opponents.

Hand B, on the other hand is a very poor overcall.  Why?
- First, even if we did want to play a minor, we are unlikely to outbid them in diamonds.
- Second, we do not want partner leading away from a diamond honor.
- Third, bidding 1♦ takes absolutely no space away from the opponents.  In fact, it offers them the chance to double to show both     majors or to bid one major to deny the other.
- Fourth, our hand is filled with singleton and doubleton honors that have dubious trick-taking potential.
- Fifth, we have length and honors in their suit, which suggests a misfit and a desire to defend.
All totaled, bidding 1♦ on Hand B rates to lose more than it gains, while bidding on Hand A rates to win more than it loses. The important lesson here is to stop being a slave to some range of points when considering whether to overcall and instead consider why you are overcalling and what you expect to gain.

At the 2-level or higher (with out a jump, natural progression (1S) - 2H by you) your overcall must be close to an opening hand (12+ HCP and always a 5+cards).  In addition, the suit should be decent.  If you have less than a full opening bid, it should only be a little less and should be compensated for by having a 6-card or longer suit.  When overcalling at higher levels, one thing to consider is your length in the opponent’s suit.  The fewer cards you have in their suit, the more likely it is that they have a fit.  If they have a fit, then it is likely that you have a fit. Therefore, the longer your suit and the shorter your holding in their suit, the safer you will be overcalling.

Responding to an overcall is similar to responding to an opening bid. You count your points, and prioritize your bidding choices the same way as you do when responding to an opening bid. However you must remember that if partner overcall on 1level they may have 8-17 points

In order of priority:

    Pass with a bad hand with out support.
    Raise partner's major suit, with support.
    Show your own major suit.
    Bid NT, with a stopper.
    Raise Partner's minor suit, with support.
    Show your own minor suit.

Overcall auctions by definition are different from uncontested auctions.  The major difference is that the opponents have stuck in a bid before you and your partner started describing your hands.  As a result, there is a suit that the opponent’s have bid.  Since the opponent’s have dared to enter the auction, we must make them pay for their audacity.  The first way that we do this is to use their bid against them.  The opponent’s suit now becomes a suit for us to cue bid.  Since we have a cue bid available, we now have multiple ways to show support.  As a result, our structure for raising partner changes.  We divide the ranges of support into at lest three different ranges.

 0-5 HCP  - Preemptive Jump Raise
 6-9 HCP  - Simple Raise
 10+ HCP - Cue Bid

If your hand falls in the 6-9 point range, then you make a simple raise to the minimum level.  

Cue Bid = Limit Raise or Better.  With 10+ points and at least 3-card support for partner’s suit, we cue bid the opponent’s suit to show our support and strength.  

Since we now have a cue bid to show 10+ points, we no longer need to jump to the 3-level to show an invitational bid.  That frees up the jump to the 3-level to show another hand.  We now use it as a preemptive raise.  It shows 4-card support with 0-5 points.    So what does this auction show?

If your partner makes a suit overcall, you are not required to bid; in fact you should pass with 0-7 points because game is out of reach. With 8-9 points you should usually respond, and with 10 points or more you must respond.

Bid a new suit when you hold a good suit of your own and have no interest in partner’s suit (you hold two cards or less). Your hand should have about 10 points or so, and you should hold a 5-card suit (or longer) with reasonable strength in your suit (partner may not have any interest in your suit either).

Bid notrump at the appropriate level when you hold a balanced hand, two cards in partner’s suit, and at least one stopper in the opponents’ suit.

Ranges for a notrump response are:

    1NT: 8 to 11 points.
    2NT: 12 to 14 points.
    3NT: 15 points or more.

There are additional factors which may influence your decision on borderline hands:
- If partner is a passed hand, do not expect partner to hold more than 10 or 11 points. If partner has not previously passed and the opponents are not competing, partner is likely to have a better hand.
- If you have a good suit of your own (that is too short to respond in), consider how many tricks that suit is likely to provide.
- If both of your opponents bid a new suit at the one level, (1C) - 1H - (1S) do not respond 1NT with less than 10 points.

Too many times a competitive auction moves along on momentum. Neither side seems to know when to sell out. The following guidelines apply to auctions where both pairs have a fit and neither side has any desire to go to game.
- Don't let the opponents play in their fit at the 2-level. It's almost always right to bid again even if you have to go to the 3 level. It's okay to go down one if the opponents were going to make their contract. They are entitled to a score and you often give them less by playing the hand and going down.
-  When the opponents are already at the 3-level, let them play there unless your side has 9 or more trumps. Bidding more in this situation will often turn the plus score you should get from setting the opponents into a minus score when you go down instead. If you think your side has the majority of strength, you can consider making a penalty double to increase the penalty you collect.
-  Don't sell out below 3 of your agreed suit when you have a 9-card fit. If the opponents compete to the 3-level, it usually works best for you to bid 3 of your suit as long as you have 9 trumps and can stay on the 3-level.
- A bid of 3 of your suit is NOT a game try if you have to go that high to win the bidding. To make a game try in a competitive auction, bid a NEW suit.
- When both sides are bidding, be willing to compete for as many tricks as your partnership has trumps. You can even compete to the 4-level with a 10-card fit. (law of total trumps).