3C

Opener has a long an powerful Club suit, at least one guard outside, and 7 or 8 playing tricks.

Responses

Responder can bid

3 of a Suit
Forcing. Responder is bidding his lowest-ranked stopper, looking for a possible NT game in the first instance. Opener responds with information about outside stoppers. May be followed by a further relay of 4D, requesting further information about features in the hand.
3NT
Natural.
Raise
To play; may be sound or speculative/preemptive.

Responses of 3 of a new suit appear below.

3D
Forcing

Shows a Diamond stopper.

Opener rebids as follows:

3H
Guard in Hearts, not in Spades.
3S
Guard in Spades, not in Hearts.
3NT
Guard in both majors.
4C
Guard in Diamonds only.

Responder may then confidently choose to play in NT; reverse into a major (forcing for one round, and a slam invitation); or make a further relay of 4D.

3H
Forcing

Shows a Heart stopper.

Opener rebids as follows:

3S
Guards in Diamonds, not Spades.
3NT
Guards in both Spades and Diamonds.
4C
No guard in Diamonds.

Responder may then confidently choose to play in NT; reverse into a major (forcing for one round, and a slam invitation); or make a further relay of 4D.

3S
Forcing

Shows a Spade stopper.

Opener rebids as follows:

3NT
Guards in both Hearts and Diamonds.
4C
At least one Red suit unguarded.

Responder may then confidently choose to play in NT; reverse into Spades (forcing for one round, and a slam invitation); or make a further relay of 4D.

After opener rebids to a new suit at the 3 level, responder can make a further relay of 4D to request further information about features in the hand. Opener rebids as follows to further describe his hand: