A first-round control is a holding which prevents the opponents from taking the first round of the suit. For example aces and voids are first round controls..

A second-round control is a holding which prevents the opponents from taking the second round of the suit. For example Kings and singletons are second round controls..

You can easily count your partnership's total point at the beginning of the auction. But, in order to determine the amount of controls in your partner's hand, you must ask it. 

Take below materials into your basket on your way to slam (or grand slam):

1. Blackwood
   Simple Blackwood
   Roman Key Card Blackwood
2. Gerber
3. Control Showing Cuebids
4. Exclusion Blackwood (Voidwood)
5. Grand Slam Force
6. DOPI and ROPI

7.1 Blackwood

Blackwood is employed to ask for aces. It is 4NT ace asking bid..

7.1.1 Simple Blackwood

4 NT is asking  partner number of aces in her hand. If your partner is asking the number of your aces by bidding 4 NT, your response will be as follows in Blackwood convention:

Your partner's bid	Your response in   Blackwood	Description of your response	Example
4 NT	5	I have 0 or 4 Ace.	4NT - 5
4 NT	5	I have 1 Ace	4NT - 5
4 NT	5	I have 2 Aces	4NT - 5
4 NT	5	I have 3 Aces	4NT - 5

After Blackwood if you determine that opponents have two aces, you can give up bidding slam by bidding your suit at the 5 level. After  you initiated Blackwood with 4 NT, your 5 NT bidding is asking the number of kings of your partner. Responses to 5 NT is same as responses to  4NT, but one level higher: Responses for the king is similiar to  above table.

Note: What must the partner who starts 4NT Blackwood bid, if he wants to play 5NT?
Whenever he bids 5NT his partner will think that he is asking the Kings..
If you want to play 5NT after your 4NT Blackwood: You must bid a strange suit at the 5 level.. This strange suit may be unbidded suit or opponents' suit.

7.1.2 Roman Key Card Blackwood

If you and your partner agreed on a trump suit in the auction 4 NT is RKBC and asks  partner's number of aces in her hand
In this convention, you accept the king of your trump suit as ace, and also you are supposed to respond 4NT so as to show your queen of trump suit.. Roman Key-Card Blackwood  also asks to show queen of trump as with king of trump.

Your partner's bid	Your response in Roman Key-Card Blackwood	Description of your response	Example
4 NT	5	I have, 0 or  3 aces.	4NT - 5
4 NT	5	I have, 1 or 4 aces.	4NT - 5
4 NT	5	I have 2 or 5 aces. I don't have queen of trump..	4NT - 5
4 NT	5	I have 2 or 5 aces. I also have queen of trump.	4NT - 5
0-3, 1-4 or 2-5 responses includes king of trump suit.  After 5 or 5 responses, you can investigate queen of trump by bidding next suit: 1) If your reply is 5 or 5 and partner bids the next suit, she is asking if you have queen of trump. 2) If the Blackwooder bids 5 NT, that means that she is asking for side suit Kings. 6C response=0 king, 6D response=1 king and 6H response=2 kings. 3) If responder has a void suit she can show it with the number of aces she has, by bidding, 5NT=2-4 key cards and 1 void 6 of a non trump suit=1-3 key cards and a void in that suit 6 of the agreed suit=1-3 key cards and a void in a higher ranking suit.    Note:There is also another version of RKCB, namely 1430 RKCB in which 5C means I have 1 or 4 , 5D means I have 0 or 3 key cards. Why the second version? It is a matter of the level you want to be after responding to RKCB..

7.2 Gerber

If you (or your partner) bid notrump at any level in the auction, you may not use 4 NT for asking number of aces your partner holds. In this case your 4 bid asks partner the number of aces she holds.Your partner's responses to yor  4 Gerber Convention is as follows:

Your partner's bid	Your response in Gerber	Description of your response	Example
4	4	I have 0 or 4 aces.	4 - 4
4	4	I have 1 ace.	4 - 4
4	4	I have 2 aces	4 - 4
4	4 NT	I have 3 aces	4 - 4NT

If the partner who initiates Gerber bids 5 , that means that he is asking the number of kings. Response to 5 is same as responses to  4 , but one level higher (at level 5). Responses for the king is similiar to above table.

7.3 Control Showing Cuebids

You can use control showing cuebids to find out which aces your partner has.  Blackwood and Gerber conventions are applied for  finding out the number of aces your partner has.. But, they are sometimes nonsense if you or your partner has  void in a suit. Control showing cuebids are  very important before starting  Blackwood.. Let's say you initiated Blackwood with a void and   doubleton as below diagram:

	- A K Q 10 7 6 A K J 10 6 7 6

Let's say your hand looks like above diagram, and, you ask the number of aces your partner holds by bidding Blackwood. Let's say she showed you one ace! If your partner has A, you have still two loosers in clubs.. So, Blackwood will not give you any information about control in clubs. In order to bid slam with above hand, you need to know if your partner has control (ace or void) in clubs. Control showing bids (these bids are also called cuebids) will give you the information you need.
Any new suit you bid, after agreed upon a trump suit, is control indicating bid. For example,  you opened one heart with a hand like in above diagram. Your partner forced to three hearts (showing 10-11 points). Any new suit you will bid will initiates  control showiing bids: But, you must start to show your controls from cheapest suit. Your four diamond bid is a control bid (cue-bid) which shows your control in diamond.  If your partner has ace of spade, she will bid four spade, if she has ace of club, she will bid five clubs in order to show her control in club. Let's say she bids five clubs. Since she was supposed to start showing her aces from cheapest one, she had to bid four spades if she was holding A. So, she has A. Since you found a control for your clubs, you can bid six hearts confidentially. If your partner bids four spade, she has A. But, she may also have two aces. Because she was supposed to initiate controllling bids from cheapest suit in her hand. Since she started with spade, she may also have club control.  In order to learn if she has also A you can start Blackwood now. If she shows one ace (definetly A), you will bid five hearts for signoff. Because, you can not take the risk of slam when your clubs are wide open to be hunted. Some few words for control bidding,

• You can still try Blackwood after control bids
• Start to bid your controlling suits from the cheapest one.
• If one of the partners determines that there is a missing control in partnership, he (or she) returns to the trump suit at the cheapest level..
• For a Grand Slam contract you must have first round control of every suit.
• If you skipped a suit and later cuebid the suit, that means that you have second-round control of that suit: 1-3- 4-4-5 (5 shows second round control)
• If the trump suit is hearts, 3 is also control showing: 1-3-3-...

Below hand diagram is taken from a championship of World Bridge Federation (http://www.worldbridge.org)

	10 6 10 6  K J 8 7 4 3 5 4 2
8 2  K 9 3 2 A 10 A K 10 9 3		A K 9 7 5  7 Q 9 Q J 8 7 4
	Q J 4 3 A Q J 8 5 4 6 5 2 --

Auction Table

W	N	E	S
-	-	1S	2H
3 C	-	4C (Trump defined)	-
4 D (Diamond control-Ace)	-	4 H  (Heart control-Singleton)	-
5 C		6 C

7.4 Exclusion Key Card Blackwood

Exclusion blackwood is not 4NT ace asking bid. Blackwood'er use his void as an ace asking bid.. 

Using Blackwood with void suits does not work.. One of the solutions is Exclusion Keycard Blackwood.. In Exclusion Blackwood you ask partner for keycards outside of the void suit... Exclusion Keycard Blackwood (or Voidwood) is used to show a void and asks partner for key cards outside the void suit. Bids which make no sense as a cue-bid is an Exclusion Keycard Blackwood:

For example a jump over game in an unbid suit or in a suit bid by the opponents.. 

5C Exclusion Blackwood shows void in Clubs 
5D Exclusion Blackwood shows void in Diamonds 
5H Exclusion Blackwood showsvoid in Hearts 
5S Exclusion Blackwood shows void in Hearts 

Responses to Exclusion Keycard Blackwood (or Voidwood) follows the same steps as RKCB-0314: For example: Next suit means I have, 0 or 3 keycards.. Below hand is taken from 6th World Junior Bridge Team Championship:

	A K 10 7 J 3 J 9 6 5 J 3 2
	J 6 5 3 A K Q 9 7 6 4 -- A 9

E	S	W	N
Pass	1 H	Pass	1 S
Pass	5 D (Exclusion)	Pass	5 NT
Pass	6 S	Pass	Pass
Pass

South accepted spades as trump suit and asked the number of keycards except diamond ace..
North has two keycards without trump queen:
5H response means 0 or 3 aces
5S response means 1 or 4 aces
5NT response means 2 keycards (Ace and King of spades) without queen of trumps!
6 C response means 2 keycards with queen of trumps..

7.5 Grand Slam Force

After you agreed a trump suit a bid of 5NT (without bidding Blackwood 4NT) bid is Grand Slam Force. Grand Slam Force asks partner to bid grand slam of the agreed trump suit if she has two of three top honors (A, K, Q). For example:

If your agreed trump is hearts, your 6 heart response to 5 NT shows that you dont have 2 top honors. But, your 7 heart response shows you have two top honors (A-K, A-Q or K-Q).

7.6 DOPI and ROPI

The D.O.P.I convention is used to respond to partner's Blackwood ace (or king) asking if RHO (Right Hand Oppenent) interfere with a suit. The letters D, O, P, I stand for,

D=Double               (after RHO's interfere with a suit
O=0                          your "double" shows zero ace)
-----------------------------------
P=Pass                  (after RHO's interfere with a suit
I=1                        your "pass" shows one ace)

The R.O.P.I convention is used to respond to partner's Blackwood ace (or king) asking if RHO (Right Hand Oppenent) interfere with double. The letters R, O, P, I stand for,

R=Redouble               (after RHO's interfere with double
O=0                          your "redouble" shows zero ace)
-----------------------------------
P=Pass                  (after RHO's interfere with double
I=1                        your "pass" shows one ace)

 

	K Q 10 4  A 10 8 2 K 4 3 A 10
8 6 5 2 7 5 4 3  J 9 8 4 3 2		- Q 9 6  A Q J 10 9 8 7 6 5 J
	A J 9 7 3 K J 2   K Q 7 6 5

South opens 1,  North bids 4NT (Blackwood),  if East bids 5, South must pass to show 1 ace...