One of the most commonly used treatments in modern bidding is the negative double. The negative double is an extremely broad topic, far beyond the scope of a single article to describe fully, but following are some important points.

In its simplest form, the negative double’s objective is to express values and length in the unbid suits — particularly the unbid major(s) — in a competitive auction. For example:

 West North East South
 1     1       Dbl

Defining East’s double as penalty is impractical: a “business” double of a one-level overcall occurs too rarely to worry about. It’s much more common to have moderate values and a heart suit after the auction begins in this manner, so most
players use the double to show a hand such as:

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By ACBL