Anopening act, also known as awarm-up act,support act,supporting act oropener, is anentertainment act (musical, comedic, or otherwise), that performs at a concert before thefeatured act, or "headliner". Rarely, an opening act may perform again at the end of the event, or perform with the featured act after both have had a set to themselves.

The opening act's performance serves to "warm up" the audience, making it appropriately excited and enthusiastic for the headliner.

Inrock music, the opening act will usually be an up-and-cominggroup with a smaller following than the headliner. On longconcert tours, different opening acts may be used for different legs of the tour.

In comedy, awarm-up comedian orcrowd warmer is astand-up comedian who performs at acomedy club or before the filming of atelevision comedy in front of astudio audience.^[1]More rarely, a comedian will open for a music concert.^[2] Their role is to make the audience feel integral to the show and encourage reactions during the show.^[3] They usually work alone and perform a comedy routine while also possibly explaining aspects of the show. In a television recording, they will also perform duringcommercial breaks.^[1] Some warm-up routines before talk shows involve giving prizes to audience members.^[3] The use of warm-ups in comedy dates back before television to radio shows.^[4]

In sports, anundercard is a preliminary bout or race between lesser known competitors, at aboxing,^[5]professional wrestling,^[6] horse racing,^[7] auto racing, or other sports event.

• Curtain raiser (drama)
• Compère
• Crowd manipulation