~Responsive Double

The “responsive double” is based on the principle that it is rarely productive to double the opponents for penalty below game level after they have found a trump fit. If partner has doubled an opening bid of one of a suit, and right hand opponent (RHO) has raised opener’s suit (through 4D), a double is for takeout, showing the unbid suits.
~After 1D, double, 3D, double: asks partner to take the double out to one of the unbid suits.
~1C, double, 2C, double: suggests equal length in the majors.
1H, double, 2H, double: you would bid spades if you had them. Here, partner is asked to pick a minor.

Bidding After the Responsive Double:
~A minimum bid shows minimum values.
~jump bids or 2NT show extra values and are invitational to game.
~A cue-bid is the only forcing bid.
~Passing a responsive double is rare.

Responsive Double After an Overcall:~If partner has made a simple suit overcall of an opponent’s 1-lvl opener and RHO has raised opener’s suit (through 4D), a double is for takeout (responsive).