Table tennis (also known as ping-pong or whiff-whaff) is a racket sport derived from tennis but distinguished by its playing surface being atop a stationary table, rather than the court on which players stand. Either individually or in teams of two, players take alternating turns returning a light, hollow ball over the table's net onto the opposing half of the court using small rackets until they fail to do so, which results in a point for the opponent. Play is fast, requiring quick reaction and constant attention, and is characterized by an emphasis on spin, which can affect the ball's trajectory more than in other ball sports.

Owed to its small minimum playing area, its ability to be played indoors in all climates, and relative accessibility of equipment, table tennis is enjoyed worldwide not just as a competitive sport, but as a common recreational pastime among players of all levels and ages.

Table tennis has been an Olympic sport since 1988, with event categories in both men's and women's singles, and men's and women's teams since replacing doubles in 2008.

Table tennis is governed by the International Table Tennis Federation (ITTF), founded in 1926, and specifies the official rules in the ITTF handbook. ITTF currently includes 226 member associations worldwide.

The sport originated in Victorian England, where it was played among the upper-class as an after-dinner parlour game. It has been suggested that makeshift versions of the game were developed by British military officers in India around the 1860s or 1870s, who brought it back with them. A row of books stood up along the center of the table as a net, two more books served as rackets and were used to continuously hit a golf-ball. In 1883, British sporting goods company Slazenger filed a patent for a net for table tennis.

The name "ping-pong" was in wide use before British manufacturer J. Jaques & Son Ltd trademarked it in 1901. The name "ping-pong" then came to describe the game played using the rather expensive Jaques's equipment, with other manufacturers calling it table tennis. A similar situation arose in the United States, where Jaques sold the rights to the "ping-pong" name to Parker Brothers. Parker Brothers then enforced its trademark for the term in the 1920s, making the various associations change their names to "table tennis" instead of the more common, but trademarked, term. The U.S. trademark for "Ping-Pong" is currently owned by Indian Industries, Inc. d/b/a Escalade Sports.

The next major innovation was by James W. Gibb, a British table tennis enthusiast, who discovered novelty celluloid balls on a trip to the US in 1901 and found them ideal for the game. This was followed by E.C. Goode who, in 1901, invented the modern version of the racket by fixing a sheet of pimpled, or stippled, rubber to the wooden blade. Table tennis was growing in popularity by 1901 to the extent that tournaments were being organized, books were being written on the subject, and an unofficial world championship was held in 1902. In those early days, the scoring system was the same as in lawn tennis.

Although both a "Table Tennis Association" and a "Ping Pong Association" existed by 1910, a new Table Tennis Association was founded in 1921, and renamed the English Table Tennis Association in 1926. The International Table Tennis Federation (ITTF) followed in 1926. London hosted the first official World Championships in 1926. In 1933, the United States Table Tennis Association, now called USA Table Tennis, was formed.

In the 1930s, Edgar Snow commented in Red Star Over China that the Communist forces in the Chinese Civil War had a "passion for the English game of table tennis" which he found "bizarre". On the other hand, the popularity of the sport waned in the 1930s Soviet Union, partly because of the promotion of team and military sports, and partly because of a theory that the game had adverse health effects.

In the 1950s, paddles that used a rubber sheet combined with an underlying sponge layer changed the game dramatically, introducing greater spin and speed. These were introduced to Britain by sports goods manufacturer S.W. Hancock Ltd. The use of speed glue beginning in the mid-1980s increased the spin and speed even further, resulting in changes to the equipment to "slow the game down". Table tennis was introduced as an Olympic sport at the Olympics in 1988.

The official rules and regulations are specified in the ITTF handbook, which was first published in 1927. The current (fiftieth) version was published in 2022.

After the 2000 Olympics in Sydney, the ITTF instituted several rule changes that were aimed at making table tennis more viable as a televised spectator sport. First, the older 38 mm (1.50 in) balls were officially replaced by 40 mm (1.57 in) balls in October 2000. This increased the ball's air resistance and effectively slowed down the game. By that time, players had begun increasing the thickness of the fast sponge layer on their paddles, which made the game excessively fast and difficult to watch on television. A few months later, the ITTF changed from a 21-point to an 11-point scoring system (and the serve rotation was reduced from five points to two), effective in September 2001. This was intended to make games more fast-paced and exciting. The ITTF also changed the rules on service to prevent a player from hiding the ball during service, in order to increase the average length of rallies and to reduce the server's advantage, effective in 2002. For the opponent to have time to realize a serve is taking place, the ball must be tossed a minimum of 16 centimetres (6.3 in) in the air. The ITTF states that all events after July 2014 are played with a new poly material ball.

The international rules specify that the game is played with a sphere having a mass of 2.7 grams (0.095 oz) and a diameter of 40 millimetres (1.57 in). The rules say that the ball shall bounce up 24–26 cm (9.4–10.2 in) when dropped from a height of 30.5 cm (12.0 in) onto a standard steel block thereby having a coefficient of restitution of 0.89 to 0.92. As of 2015, balls are now made of a polymer instead of celluloid, colored white or orange, with a matte finish. The choice of ball color is made according to the table color and its surroundings. For example, a white ball is easier to see on a green or blue table than it is on a grey table. Manufacturers often indicate the quality of the ball with a star rating system, usually from one to three, three being the highest grade. As this system is not standard across manufacturers, the only way a ball may be used in official competition is upon ITTF approval (the ITTF approval can be seen printed on the ball).

The 40 mm ball was introduced after the end of the 2000 Summer Olympics; previously a 38 mm ball was standard. This created some controversies. Vladimir Samsonov, the World No. 1 table tennis professional at the time, threatened to pull out of the World Cup, which was scheduled to debut the new regulation ball on 12 October 2000.

The table is 2.74 m (9.0 ft) long, 1.525 m (5.0 ft) wide, and 76 cm (2.5 ft) high with any continuous material so long as the table yields a uniform bounce of about 23 cm (9.1 in) when a standard ball is dropped onto it from a height of 30 cm (11.8 in), or about 77%. The table or playing surface is uniformly dark colored and matte, divided into two halves by a net at 15.25 cm (6.0 in) in height. The ITTF approves only wooden tables or their derivates. Concrete tables with a steel net or a solid concrete partition are sometimes available in outside public spaces, such as parks.

ITTF regulations require a playing space of at least 14 m (45.9 ft) long by 7 m (23.0 ft) wide, and a height clearance of at least 5 m (16.4 ft). For wheelchair events, the minimums are 8 m (26.2 ft) long and 6 m (19.7 ft) wide.

Players are equipped with a laminated wooden racket covered with rubber on one or two sides depending on the grip of the player. The ITTF uses the term "racket", though "bat" is common in Britain, and "paddle" in the U.S. and Canada.

The wooden portion of the racket, often referred to as the "blade", commonly features anywhere between one and seven plies of wood, though cork, glass fiber, carbon fiber, aluminum fiber, and Kevlar are sometimes used. According to the ITTF regulations, at least 85% of the blade by thickness shall be of natural wood. Common wood types include balsa, limba, cypress, and hinoki, which is popular in Japan. The average size of the blade is about 17 centimetres (6.7 in) long and 15 centimetres (5.9 in) wide. Although the official restrictions only focus on the flatness and rigidity of the blade itself, these dimensions are optimal for most play styles.

Table tennis regulations allow different rubber surfaces on each side of the racket. Various types of surfaces provide various levels of spin or speed, and in some cases they nullify spin. For example, a player may have a rubber that provides much spin on one side of their racket, and one that provides no spin on the other. By flipping the racket in play, different types of returns are possible. To help a player distinguish between the rubber used by his opposing player, international rules specify that one side must be black while the other side must be a bright color clearly distinguishable from black and from the color of the ball. The player has the right to inspect their opponent's racket before a match to see the type of rubber used and what color it is. Despite high-speed play and rapid exchanges, a player can see clearly what side of the racket was used to hit the ball. Current rules state that, unless damaged in play, the racket cannot be exchanged for another racket at any time during a match.

According to ITTF rule 2.13.1, the first service is decided by lot, normally a coin toss. It is also common for one player (or the umpire/scorer) to hide the ball in one or the other hand, usually hidden under the table, allowing the other player to guess which hand the ball is in. The correct or incorrect guess gives the "winner" the option to choose to serve, receive, or to choose which side of the table to use. (A common but non-sanctioned method is for the players to play the ball back and forth three times and then play out the point. This is commonly referred to as "serve to play", "rally to serve", "play for serve", or "volley for serve". Another common method is referred to as "Ping for serve" or "Pinging for serve" where players will begin playing by hitting or bouncing the ball and playing a rally spelling out the word ping P-I-N-G with each hit then playing out the point for service).

In game play, the player serving the ball commences a play. The server first stands with the ball held on the open palm of the hand not carrying the paddle, called the freehand, and tosses the ball directly upward without spin, at least 16 cm (6.3 in) high. The server strikes the ball with the racket on the ball's descent so that it first touches the server's court, and then touches directly the receiver's court without touching the net assembly. In casual games, many players do not toss the ball upward; however, this is technically illegal and can give the serving player an unfair advantage.

The ball must remain behind the endline and above the playing surface of the table at all times during the service. The server's body or clothing cannot be used to obstruct sight of the ball; the opponent and the umpire must have a clear view of the ball at all times. If the umpire is doubtful of the legality of a service they may first interrupt play and give a warning to the server. If the serve is a clear failure or is doubted again by the umpire after the warning, the receiver scores a point.

If the service is "good", then the receiver must make a "good" return by hitting the ball back before it bounces a second time on receiver's side of the table so that the ball passes the net and touches the opponent's court, either directly or after touching the net assembly. Thereafter, the server and receiver must alternately make a return until the rally is over. Returning the serve is one of the most difficult parts of the game, as the server's first move is often the least predictable and thus most advantageous shot due to the numerous spin and speed choices at the server's disposal.

A let is a rally of which the result is not scored, and is called in the following circumstances:

• The ball touches the net in service (service), provided the service is otherwise correct or the ball is obstructed by the player on the receiving side. Obstruction means a player touches the ball when it is above or traveling towards the playing surface, not having touched the player's court since last being struck by the player.
• When the player on the receiving side is not ready and the service is delivered.
• Player's failure to make a service or a return or to comply with the Laws is due to a disturbance outside the control of the player.
• Play is interrupted by the umpire or assistant umpire.

A let is also called foul service, if the ball hits the server's side of the table, if the ball does not pass further than the edge, and if the ball hits the table edge and hits the net.

A point is scored by the player for any of several results of the rally:

• The opponent fails to make a correct service or return.
• After making a service or a return, the ball touches anything other than the net assembly before being struck by the opponent.
• The ball passes over the player's court or beyond their end line without touching their court, after being struck by the opponent.
• The opponent obstructs the ball.
• The opponent strikes the ball twice successively. The hand that is holding the racket counts as part of the racket and that making a good return off one's hand or fingers is allowed. It is not a fault if the ball accidentally hits one's hand or fingers and then subsequently hits the racket.
• The opponent strikes the ball with a side of the racket blade whose surface is not covered with rubber.
• The opponent moves the playing surface or touches the net assembly.
• The opponent's free hand touches the playing surface.
• As a receiver under the expedite system, completing 13 returns in a rally.
• The opponent that has been warned by the umpire commits a second offense in the same individual match or team match. If the third offence happens, 2 points will be given to the player. If the individual match or the team match has not ended, any unused penalty points can be transferred to the next game of that match.

A game shall be won by the player first scoring 11 points unless both players score 10 points, when the game shall be won by the first player subsequently gaining a lead of 2 points. A match shall consist of the best of any odd number of games. In competition play, matches are typically best of five or seven games.

Service alternates between opponents every two points (regardless of winner of the rally) until the end of the game, unless both players score ten points or the expedite system is operated, when the sequences of serving and receiving stay the same but each player serves for only one point in turn (Deuce). The player serving first in a game receives first in the next game of the match.

After each game, players switch sides of the table. In the last possible game of a match, for example the seventh game in a best of seven match, players change ends when the first player scores five points, regardless of whose turn it is to serve. If the sequence of serving and receiving is out of turn or the ends are not changed, points scored in the wrong situation are still calculated and the game shall be resumed with the order at the score that has been reached.

In addition to games between individual players, pairs may also play table tennis. Singles and doubles are both played in international competition, including the Olympic Games since 1988 and the Commonwealth Games since 2002.

In doubles, all the rules of single play are applied except for the following.

Service

A line painted along the long axis of the table to create doubles courts bisects the table. This line's only purpose is to facilitate the doubles service rule, which is that service must originate from the right hand "box" in such a way that the first bounce of the serve bounces once in said right hand box and then must bounce at least once in the opponent side's right hand box (far left box for server), or the receiving pair score a point.

Order of play, serving and receiving

1. Players must hit the ball in turn. For example, if A is paired with B and X is paired with Y, then A is the server and X is the receiver. and the order of play shall be A→X→B→Y. The rally proceeds this way until one side fails to make a legal return and the other side scores.
2. At each change of service, the previous receiver shall become the server and the partner of the previous server shall become the receiver. For example, if the previous order of play is A→X→B→Y, the order becomes X→B→Y→A after the change of service.
3. In the second or the latter games of a match, the game begins in reverse order of play. For example, if the order of play is A→X→B→Y at beginning of the first game, the order begins with X→A→Y→B or Y→B→X→A in the second game depending on either X or Y being chosen as the first server of the game. That means the first receiver of the game is the player who served to the first server of the game in the preceding game. In each game of a doubles match, the pair having the right to serve first shall choose which of them will do so. The receiving pair, however, can only choose in the first game of the match.
4. When a pair reaches 5 points in the final game, the pairs must switch ends of the table and change the receiver to reverse the order of play. For example, when the last order of play before a pair score 5 points in the final game is A→X→B→Y, the order after change shall be A→Y→B→X if A still has the second serve. Otherwise, X is the next server and the order becomes X→A→Y→B.

If a game is unfinished after 10 minutes of play and fewer than 18 points have been scored, the expedite system is initiated. The umpire interrupts the game, and the game resumes with players serving for one point in turn. If the expedite system is introduced while the ball is not in play, the previous receiver shall serve first. Under the expedite system, the server must win the point before the opponent makes 13 consecutive returns or the point goes to the opponent. The system can also be initiated at any time at the request of both players or pairs. Once introduced, the expedite system remains in force until the end of the match. As it is intended as a rule to shorten the duration of a match, it is mainly deployed in defensive players' matches, which tend to have longer points.

Though table tennis players grip their rackets in various ways, their grips can be classified into two major families of styles, penhold and shakehand. The rules of table tennis do not prescribe the manner in which one must grip the racket, and numerous grips are employed.

The penhold grip is so-named because one grips the racket similarly to the way one holds a writing instrument. The style of play among penhold players can vary greatly from player to player. The most popular style, usually referred to as the Chinese penhold style, involves curling the middle, ring, and fourth finger on the back of the blade with the three fingers always touching one another. Chinese penholders favour a round racket head, for a more over-the-table style of play. In contrast, another style, sometimes referred to as the Japanese/Korean penhold grip, involves splaying those three fingers out across the back of the racket, usually with all three fingers touching the back of the racket, rather than stacked upon one another. Sometimes a combination of the two styles occurs, wherein the middle, ring and fourth fingers are straight, but still stacked, or where all fingers may be touching the back of the racket, but are also in contact with one another. Japanese and Korean penholders will often use a square-headed racket for an away-from-the-table style of play. Traditionally these square-headed rackets feature a block of cork on top of the handle, as well as a thin layer of cork on the back of the racket, for increased grip and comfort. Penhold styles are popular among players originating from East Asian countries such as China, Japan, South Korea, and Taiwan.

Traditionally, penhold players use only one side of the racket to hit the ball during normal play, and the side which is in contact with the last three fingers is generally not used. This configuration is sometimes referred to as "traditional penhold" and is more commonly found in square-headed racket styles. However, the Chinese developed a technique in the 1990s in which a penholder uses both sides of the racket to hit the ball, where the player produces a backhand stroke (most often topspin) known as a reverse penhold backhand by turning the traditional side of the racket to face one's self, and striking the ball with the opposite side of the racket. This stroke has greatly improved and strengthened the penhold style both physically and psychologically, as it eliminates the strategic weakness of the traditional penhold backhand.