Performance by an Actor in a Supporting Role is one of the Academy Awards of Merit presented annually by the Academy of Motion Picture Arts and Sciences (AMPAS) to recognize an actor who has delivered an outstanding performance while working within the film industry. Since its inception, however, the award has commonly been referred to as the Oscar for Best Supporting Actor. While actors are nominated for this award by Academy members who are actors and actresses themselves, winners are selected by the Academy membership as a whole.

Throughout the past 76 years AMPAS has presented a total of 76 Best Supporting Actor awards to 69 different actors. Winners of this Academy Award of Merit receive the familiar Oscar statuette, depicting a gold-plated knight holding a crusader's sword and standing on a reel of film. Prior to the 16th Academy Awards ceremony (1943), however, they received a plaque. The first recipient was Walter Brennan, who was honored at the 9th Academy Awards ceremony (1936) for his performance in Come and Get It. The most recent recipient was Christopher Plummer, who was honored at the 84th Academy Awards ceremony (2012) for his performance in Beginners.

A supporting actor is an actor who performs roles in a play or film other than that of the leads.

These roles range from bit parts to secondary leads. They are sometimes but not necessarily character roles. A supporting actor must also use restraint not to upstage the main actor/actress in the play/movie. In earlier times these were often ethnic stereotypes. The title is usually specific to the performance, that is, a person may be a supporting actor in one film and the leading actor in the next. An individual who typically plays supporting roles is considered a character actor.

In television, a day player refers to most performers with supporting speaking roles hired on a daily basis without long-term contracts.

Supporting roles may be pivotal or vital to the story. In recognition of important nature of this work, the theater and film industries give separate awards to the Best Supporting Actor and actress. A supporting actor/actress can also be known as a 'sidekick'.

An Academy Award is an award bestowed by the American Academy of Motion Picture Arts and Sciences (AMPAS) to recognize excellence of professionals in the film industry, including directors, actors and writers. The Oscar statuette is officially named the Academy Award of Merit and is one of nine types of Academy Awards.

The formal ceremony at which the Awards of Merit are presented is one of the most prominent award ceremonies in the world, and is televised live in more than 100 countries annually. It is also the oldest award ceremony in the media; its equivalents, the Grammy Awards (for music), Emmy Awards (for television), and Tony Awards (for theatre) are modeled after the Academy.

The AMPAS was originally conceived by Metro-Goldwyn-Mayer studio boss Louis B. Mayer as a professional honorary organization to help improve the film industry’s image and help mediate labor disputes. The Oscar itself was later initiated by the Academy as an award "of merit for distinctive achievement" in the industry.