A double act, also known as a comedy duo, is a comic pairing in which humor is derived from the uneven relationship between two partners, usually of the same gender, age, ethnic origin and profession, but drastically different personalities or behavior. Often one of the duo members, the straight man, feed, dead wood, or stooge is portrayed as reasonable and serious, and the other one, the funny man, banana man or comic is portrayed as funny, less educated or less intelligent, silly, or unorthodox. If the audience identifies primarily with one character, the other is often referred to as a comic foil. The term feed comes from the way a straight man will set up jokes for—or "feed" them to—their partner.

Despite the names given to the roles, the "straight man" need not necessarily be humorless, and it is not always the comic who provides the act's humor. Sometimes, it is the straight man who gets the laughs through his or her sarcastic reactions to the comic's antics, as was often the case with Stewart Lee's deadpan, reasoned reactions to Richard Herring's more ridiculous antics in their pairing. Where the "straight man" serves no personal comic purpose but acts as a device to make the "comic" look good, they are known as a "Stooge". This is sometimes considered a derogatory term. Most often, however, the humor in a double act comes from the way the two personalities play off each other rather than the individuals themselves; in many successful acts the roles are interchangeable.