In tennis, an official is a person who ensures that a match or tournament is conducted according to the International Tennis Federation Rules of Tennis and other competition regulations.^[2]

At the highest levels of the sport, a team of up to eleven officials may be on court at any given time.^[3] These officials are broken up into categories based on their responsibility during the match. Contrastingly, many tennis matches are conducted with no officials present directly on court.

Tennis officials are certified by their respective national associations. The ITF also certifies officials in the categories of the chair umpire, referee and a chief umpire.^[4] Each ITF certification or "badge" is broken into five certification levels. The first, green badge, is considered sufficient for officiating at the highest levels of tennis within the official's own nation and is not divided into categories (and is primarily used in Spanish- and French-speaking areas, where a national organization may not be present). The second, the white badge, is divided into three categories (chair, chief, and referee) but remains only a national certification. The following three, bronze (chair umpire only), silver, and gold badge are considered international certifications. These international officials are those seen at the highest levels of play like the Grand Slams, ATP and WTA Tours, and the Fed and Davis Cups.^[5]

The chair umpire is the final authority on all questions of fact during the match. Questions of fact include whether a ball was in, the calling of a service let or the calling of a foot-fault. In matches where line umpires are also assigned, the chair umpire has the right to overrule if a clear mistake has been made. The chair umpire is often situated in a tall chair at the centre of the court, behind a net post. The players' benches are to either side of the chair. From this position, the chair umpire calls the score of the match to the players and spectators between points. At the conclusion of a point, game, or set, the chair umpire times the players to ensure they follow ITF regulations on pace of play. The chair umpire is responsible for completing a scorecard, the official historical record of the match.

The line umpire (or line judge) "calls all shots relating to the assigned lines."^[6] Line umpires work on court as part of a team of between one and nine line umpires. Each line umpire is assigned to one line or, in the case of a short-handed crew, a position in a system. For example, a line umpire on the receiver's side may have to cover the center service line then, following the service, move to one of the sidelines.

The line umpire signals a ball out by making a verbal "out" call ("fault" for a serve) followed by the extension of the arm shoulder high in the direction the ball was out. A ball is signalled "safe" or "good" by holding both hands together knee-high in front of the body.^[7] A line umpire who is unable to call a shot (usually because a player obstructs their view) signals this by holding their hands beside their head, the upper side pointing in the same direction as the eyes; that call is then the chair umpire's responsibility. Line umpires are also responsible for calling foot faults. When baseline umpires are being used, they watch to see if the server touches any part of the baseline before the ball is struck. Center service line umpires are responsible for calling foot faults when the server steps over the imaginary extension of the centerline. Footfault calls are made with a verbal "Footfault" call followed by a vertical extension of the arm with the palm open.

To reduce staff due to COVID-19 pandemic restrictions, the 2020 US Open employed electronic line judges on most matches, excluding those held at Arthur Ashe Stadium and Louis Armstrong Stadium. At the 2021 Australian Open, all matches used electronic line judges for the first time in a Grand Slam event.^[8][9]

• List of tennis umpires, current and former.
• Electronic line judge