Go is a strategic, two-player board game originating in ancient China between 2000 BC and 200 BC.

Go is a popular game in East Asia. The development of Internet play has increased its popularity throughout the rest of the world. The English name Go originated from the Japanese character 碁 (go), though it is usually called 囲碁 (igo) in Japanese. The Chinese name 圍棋 (trad.) / 围棋 (simp.) (pinyin: wéiqí) roughly translates to the "Board Game of Surrounding (Territory)", or, less literally, the "Enclosing Game". Its ancient Chinese name is 弈 (pinyin: yì),and is also listed under 碁 in the Kangxi Dictionary. It is also known as 바둑 (baduk) in Korean.

Overview of the Game 

The two players, black and white, battle to maximize the territory they control, seeking to surround large areas of the board with their stones, to capture any opposing stones that invade these areas, and to protect their own stones from capture. The strategy involved can become very subtle and sophisticated.

Go is typically classified as an abstract board game. However, a resemblance between the game of Go and war is often suggested. The Chinese classic The Art of War ????, for instance, has sometimes been applied to Go strategy as well. On the other hand, general strategies of Go are well described by proverbs and are applied in other contexts such as management.

Real wars end when the participants sign treaties. Likewise, in Go, the players have to agree that the game has ended. Only then is the score and the winner finally determined.

Basic rules

If white plays at A, the black chain loses its last liberty, and is captured and removed from the board.


Two players, black and white, take turns placing a stone (game piece) on the points (intersections) of a 19 by 19 board (grid). Black moves first. 

Stones must have liberties (empty adjacent points) to remain on the board. Stones connected by lines are called chains, and share their liberties. 
When a stone or a chain of stones is surrounded by opponent stones, so that it has no more liberties, it is captured and removed from the board. 
If a stone has no liberties as soon as it is played, but simultaneously removes the last liberty from one or more of the opponent's chains, the opponent's chains are captured and the played stone is not. 
"Ko rule": A stone cannot be played on a particular point, if doing so would recreate the board position that existed after the same player's previous turn. 
A player may pass instead of placing a stone. When both players pass consecutively, the game ends and is then scored. 
A player's score is the number of empty points enclosed only by his stones plus the number of points occupied by his stones. The player with the higher score wins. 
This is the essence of the game of Go. The possibility and threat to capture opposing stones provides strategic variation and makes the game interesting. (Also see strategy.)

For a more detailed treatment, see Rules of Go. Note in particular that there are other rulesets which count the score differently, yet almost always produce the same result.

Go allows one to play not only even games (games between players of roughly equal strength) but also handicap games (games between players of unequal strength)

Optional rules
Optional Go rules may set the following:

compensation points, almost always for the second player, see komi; 
compensation stones ("handicap") placed on the board before alternate play, allowing players of different strengths to play interesting games (see handicap go). 

Strategy
Main article: Go strategy and tactics 
Basic strategic aspects include the following:

Connection: Keeping one's own stones connected means that fewer groups need defense. 
Cut: Keeping opposing stones disconnected means that the opponent needs to defend more groups. 
Life: This is the ability of stones to avoid their removal. Usually life requires at least two "eyes" for a group of stones. 
Death: The absence of life, resulting in the removal of a group. 

Nature of the game
Although rules of Go can be written so that they are very simple, the game strategy is extremely complex. Go is a complete-knowledge, deterministic, strategy game: in the same class as chess, checkers (draughts), and reversi. Its depth arguably exceeds even those games. Its large board and lack of restrictions allows great scope in strategy. Decisions in one part of the board may be influenced by an apparently unrelated situation, in a distant part of the board. Plays made early in the game can shape the nature of conflict a hundred moves later.

The game emphasises the importance of balance on multiple levels, and has internal tensions. To secure an area of the board, it is good to play moves close together; but to cover the largest area one needs to spread out. To ensure one does not fall behind, expansionist play is required; but playing too broadly leaves weaknesses undefended that can be exploited. Playing too low (close to the edge) secures insufficient territory; yet playing too high (far from the edge) allows the opponent to invade. Many people find the game attractive for its reflection of polarities also found in life.

See Go strategy and tactics for an introductory explanation of how to play well.

It is commonly said that no game has ever been played twice. This may be true: On a 19×19 board, there are about 3361×0.012 = 2.1×10170 possible positions, most of which are the end result of about (120!)2 = 4.5×10397 different (no-capture) games, for a total of about 9.3×10567 games. Allowing captures gives as many as


possible games, all of which last for over 4.1×1048 moves! (For two comparisons: the number of legal positions in chess is estimated to be between 1043 and 1050; and physicists estimate that there are not more than 1090 protons in the entire visible universe.)


Philosophy
According to legend, the game was used as a teaching tool after the ancient Chinese emperor Yao 堯 (2337 - 2258 BC) designed it for his son, Danzhu, who he thought needed to learn discipline, concentration, and balance. Another suggested genesis for the game states that in ancient times, Chinese warlords and generals would use pieces of stone to map out attacking positions. Further and more plausible theories relate Go equipment to divination or flood control. See also history of Go.

Before the industrial age in China, Go was perceived as the game of the aristocratic class while xiangqi (Chinese chess) was perceived as the game of the masses. Go was considered one of the cultivated arts of the Chinese scholar gentleman, along with Chinese calligraphy, Chinese painting and playing the Guqin, known as 琴棋書畫, or the Four Arts of the Chinese Scholar.

Go is deep, as playing against any stronger player will demonstrate (depth of the game as established by ELO ranking in Go). With each new level (rank) comes a deeper appreciation for the subtlety involved, and for the insight of stronger players. Beginners often start by randomly placing stones on the board, as if it were a game of chance — and they inevitably lose to experienced players. But soon an understanding of how stones connect to form strength develops, and shortly afterward a few basic common opening sequences may be understood. Learning the ways of life and death helps to develop one's situational judgement.

Further experience yields an understanding of the board, the importance of the edges, then the efficiency of developing (in the corners first, then sides, then centre). Soon, the advanced beginner understands that territory and influence are somewhat interchangeable — but there needs to be a balance. Best is to develop more or less at the same pace as the opponent, in both territory and influence. This intricate struggle of power and control makes the game highly dynamic.


Computers and Go
Main article: Computer Go 
Although attempts have been made to program computers to play Go, success in that area has been moderate at best — development in this area has not reached the level of Chess programs. Even the strongest programs are no better than an average club player, and would easily be beaten by a strong player even getting a nine-stone handicap. (In fact, it is not uncommon for computers to be beaten by strong players at handicaps of twenty-five stones. It would probably be extremely common except that many Go players think it beneath them to play computers.) This is attributed to many qualities of the game, including the "optimising" nature of the victory condition, the virtually unlimited placement of each stone, the large board size (but it would be misleading to say they cope better on smaller boards), the nonlocal nature of the Ko rule, and the high degree of pattern recognition involved. For this reason, many in the field of artificial intelligence consider Go to be a better measure of a computer's capacity for thought than chess.

Use of computer networks to allow humans to meet, discuss games, and play one another, although generally considered inferior to face-to-face play, is becoming much more common. There are servers and software to facilitate this; see Additional Resources below for more information.


Other board games sometimes compared with Go
This is a list of some games that are played with similar equipment or come from the same area.

Variations of chess 
Western chess: This game dominates Western game culture; its history in the culture stretches back many centuries. 
Shogi 将棋: Early Western literature often referred to Go as "Japanese Chess". The Japanese do have their own game called Shogi; it is much more similar to the other Chess variants than to Go. Shogi schools were founded in Japan about the same time as Go schools, but the game never received as much favour as Go. 
Xiangqi 象棋: This is the Chinese variant of Chess, usually called "Chinese chess" by English speakers. Like most Chess variants, it has great depth of strategy, but bears few similarities to Go in game play. Xiangqi, like Go, is played on points rather than squares. 
Janggi: This is the Korean variant of Chess, usually called "Korean Chess". It is also very different from Go in game play. Go and Janggi are the two main board games played in Korea. 
The Game of the Amazons: A cross between Go and Chess. In this game the pieces have the same movements as the Queen in Chess. After a player moves, the piece fires an arrow (that has the same movement as a Queen in Chess). An arrow blocks the paths of other pieces and arrows. The player who can move last wins. There can never be a draw. 
Connection games. These are the most similar to Go in terms of style and strategy. One significant difference between Go and many connection games is the number of goals. In Hex, for example, there is only one goal: to connect your two sides. While this leads to significant strategic complexity (especially as the board size increases), in Go there are usually numerous different battles going on simultaneously. 
Hex and TwixT are connection games. Like Go, these have cutting and connecting tactics, but Hex is played on a hexagonal lattice. 
Y, Havannah, and *Star are connection games similar to Hex, but of more depth. 
Reversi: Marketed by Mattel as "Othello", Reversi bears superficial similarity to Go, with black and white circular pieces, an undifferentiated grid for a board, simple rules, and a goal of covering more of the board than the opponent. The game play is quite unlike Go, however, as it is based on flanking the opponent's pieces for capture. Captured pieces change their color. 
Gomoku, Renju and Pente: Played with the same equipment as Go (a 19x19 grid, black and white stones), in these games the goal is to create five stones in a row. The game style is thus much shorter and involves less strategy than Go. 
Abalone is a board game with black and white marbles. Strategy is somewhat of a cross between Reversi and Sumo wrestling, the goal being to push the other player's marbles off the playing surface. 
Alak is a Go-like game restricted to a single spatial dimension. 

Traditional Go game equipment

Although one could play Go with a piece of cardboard for a board and a bag of plastic tokens, many Go players pride themselves on their game sets.

The traditional Go board (called a goban 碁盤 in Japanese) is solid wood with a hollowed underside, about 15–20 cm thick, and stands on its own attached legs. It is preferably made from the rare golden-tinged Kaya tree (Torreya nucifera), with the very best made from Kaya trees up to 700 years old.

Players sit on reed mats (tatami) on the floor to play. The stones (go-ishi 碁石) are kept in matching solid wood pots (go-ke 碁笥) and are made out of clamshell (white) and slate (black) and are extremely smooth. The natural resources of Japan have been unable to keep up with the enormous demand for the native clams and slow-growing Kaya trees; both must be of sufficient age to grow to the desired size, and they are now extremely rare at the age and quality required, raising the price of such equipment tremendously.

In clubs and at tournaments, where large numbers of sets must be maintained (and usually purchased) by one organization, the expensive traditional sets are not usually used. For these situations, table boards (of the same design as floor boards, but only about 2–5 cm thick and without legs) are used, and the stones are made of glass rather than slate and shell. Bowls will often be plastic if wooden bowls are not available. Plastic stones could be used, but are considered inferior to glass as they are generally much lighter, and most players find that not even the lower price justifies their unpleasantness. Very high quality table boards can be made of Kaya. Other woods often used to make quality table boards include Hiba (Thujopsis dolabrata), Katsura 桂 (Cercidiphyllum japonicum), and Agathis.

Traditionally, the board's grid is 1.5 shaku 尺 long by 1.4 shaku wide (455 mm by 424 mm) with space beyond to allow stones to be played on the edges and corners of the grid. This often surprises newcomers: it is not a perfect square, but is longer than it is wide, in the proportion 15:14. Two reasons are frequently given for this. One is that when the players sit at the board, the angle at which they view the board gives a foreshortening of the grid; the board is slightly longer between the players to compensate for this. Another suggested reason is that the Japanese aesthetic finds structures with geometric symmetry to be in bad taste.

Traditional stones are made so that black stones are slightly larger in diameter than white; this is probably to compensate for the optical illusion created by contrasting colours that would make equal-sized white stones appear larger on the board than black stones. The difference is slight, and since its effect is to make the stones appear the same size on the board, it can be surprising to discover they are not.

The bowls for the stones are of a simple shape, like a flattened sphere with a level underside. The lid is loose-fitting and is upturned before play as a tray to collect stones captured during the game. The bowls are usually made of turned wood, although small lidded baskets of woven bamboo or reeds make an attractive cheaper alternative.

There is even an art to placing a Go stone, held between the tips of the outstretched index and middle fingers and striking the board firmly to create a sharp click. Many consider the acoustic properties of the wood of the board to be quite important. The traditional goban will usually have its underside carved with a pyramid called a heso recessed into the board. Tradition holds that this is to give a better resonance to the stone's click, but the more conventional explanation is to allow the board to expand and contract without splitting the wood. A board is seen as more attractive when it is marked with slight dents from decades – or centuries – of stones striking the surface.

On smaller boards, a handicap may still be used, but it is reduced proportionally relative to the area of the board. For example, if a player takes 8 stones against another player on a 19 x 19 board (361 points), they would take 4 stones on a 13 x 13 board (169 points or approximately half) and 2 stones on a 9 x 9 board (81 points or approximately 1/4). Smaller boards are typically used for beginners learning the game.


The Go world

Ranks

In countries where Go is popular, ranks are employed to indicate playing strength. From about the sixteenth century, the Japanese formalised the teaching and ranking of Go. The system is comparable to that of martial arts schools; and is considered to be derived ultimately from court ranks in China.

Beginning players today start at a rank of between 25 and 30 kyu 級. The kyu ranking then decreases in magnitude as the player becomes stronger, dropping down to 1 kyu or 1k. Since beginners will commonly progress through elementary concepts quickly, it may be difficult to set a solid kyu ranking for new players. Players who have progressed through the kyu ranks and passed the 1 kyu mark are then ranked at 1 dan 段 or 1d, sometimes called shodan. The player then could advance through the amateur dan ranks up to amateur 7 dan, which only few players achieve. That playing level is roughly equivalent to where the ranks for professionals start with pro 1 dan going up to 9 dan (also sometimes called ping or p as in 9 p to avoid confusion between a 1 dan professional and a weaker amateur 6 dan). The distinction between each amateur rank is, by definition, one handicap stone. Professional ranks are awarded by professional organizations and though they are less well defined, they are closer, so that the difference between an average 1p and a prime 9p may be three handicap stones (however, tournament games are even).

In other words, the difference in rank between two players is theoretically equal to the number of handicap stones required for each player to have an even chance of winning. Beating this handicap consistently is the indicator that a player's strength has improved, and his rank should be adjusted upward by one stone, thus changing the number of handicap stones required.


Timing
Like many other games, a game of Go may be timed. There are four typical methods of timing a game:

Absolute: a specific amount of time is given for the entire game, regardless of how fast or slow each player is. This is extremely rare. 
Byo-Yomi (Japanese Timing): After the main time is depleted, a player has a certain number of time periods (typically around 30 seconds). After each move, the number of time periods that the player took (possibly zero) is subtracted. For example, if a player has three 30-second time periods and takes 30 or more (but less than 60) seconds to make a move, he loses one time period. With 60-89 seconds, he loses two time periods, and so on. If, however, he takes less than 30 seconds, the timer simply resets without subtracting any periods. This is written as <maintime> + <byo-yomi time period>x<number of byo-yomi time periods>. 
Canadian Byo-Yomi: After the main time is depleted a player must make a certain number of moves within a certain period of time. For example, 5 moves within 2 minutes. If 5 moves are made in time, the timer resets to 2 minutes again. This is written as <main time>/<byo-yomi time period>/<number of moves to be completed in each byo-yomi time period>. (The Origins of Canadian Byo-Yomi) 
Progressive Byo-Yomi: usually this is based on Canadian Byo-Yomi, where after main time is depleted the first number of moves must be played in a time, but the next number of moves may be different and played in a different amount of time. For instance, in one amateur tournament the main time of 50 minutes was followed by twenty moves in five minutes, then forty moves in five minutes, then sixty moves in five minutes (the last time period being repeated until the game ended). Thus, this tournament's timing was written 50+20/5+40/5+60/5 (it is common to leave minutes as numbers without units while seconds are usually written in the form 5s). 
Japanese Timing is equivalent to Canadian Byo-Yomi when the "certain number of moves" is equal to one.


Top players
Main article: Go players 
Although the game was developed in China, in recent centuries the strongest of the players in the world have come from Japan. However, top players from China (since the 1980s) and South Korea (since the 1990s) have reached an even higher level. Nowadays, top players from these three countries are of comparable strength, although top Korean players seem to have an edge, dominating the major international titles, winning 23 tournaments in a row between 2000 and 2002. All three countries have a number of professional Go tournaments. The top Japanese tournaments have a prize purse comparable to that of professional golf tournaments in the United States. Tournaments in China and Korea are less lavishly funded.

Players from other countries have traditionally been much weaker, except for some players who have taken up professional courses in one of the Asian countries. This is attributable to the fact that details of the game have been unknown outside of Asia for most of the game's history. A German scientist, Otto Korschelt, is credited with the first systematic description of the game in a Western language in AD 1880; it was not until the 1950s that Western players would take up the game as more than a passing interest. In 1978, Manfred Wimmer became the first Westerner to receive a professional player's certificate from an Asian professional Go association. It was not until 2000 that a Westerner, Michael Redmond, achieved the top rank awarded by an Asian go association.

Top male players are stronger than top female players on average.


History
Main article: History of Go 

Early in the 17th century, the then best player in Japan, Honinbo Sansa, was made head of a newly founded Go academy (the Honinbo school, the first of several competing schools founded about the same time), which developed the level of playing greatly, and introduced the martial-arts style system of ranking players. The government discontinued its support for the Go academies in 1868 as a result of the fall of the Tokugawa shogunate.

In honour of the Honinbo school, whose players consistently dominated the other schools during their history, one of the most prestigious Japanese Go championships is called the "Honinbo" tournament.

Historically, Go has been unequal in terms of gender. However, the opening of new, open tournaments and the rise of strong female players, most notably Rui Naiwei, has in recent years legitimised the strength and competitiveness of emerging female players.

Around 2000, in Japan, the manga (Japanese comic) and anime series Hikaru no Go has popularized Go among the youth and started a Go boom in Japan. In January 2004, the Hikaru no Go manga also began running in the American periodical Shonen Jump. Whether this will lead to a strong following in the US is yet to be seen.

Scott A. Boorman's The Protracted Game: A Wei-Chi Interpretation of Maoist Revolutionary Strategy likens the game to historical events, saying that the Maoists were better at surrounding territory.


Mathematical theory of Go endgames
Elwyn Berlekamp and David Wolfe have developed a mathematical theory of the late endgame in Go based on the combinatorial game theory of John Horton Conway. It is outlined in their book, Mathematical Go (ISBN 1568810326). Whilst not of general utility in most play, it greatly aids the analysis of certain classes of positions.

It is worth noting that Conway developed the mathematical concept of surreal numbers while studying Go endgames.


Go in popular culture

Go has been mentioned in many novels and short stories published in the Orient, and occasionally turns up in Western media as well.

In 1951, Nobel Prize-winning author Yasunari Kawabata published The Master of Go, a short novel based upon an epic game that took place over the course of several months in 1938. An English translation appeared in 1972, around the time of Kawabata's death. Go also features (as "Wei-ch'i") as a favourite pastime of and philosophical inspiration for the archvillan Howard Devore in the Chung Kuo novels by David Wingrove.

Go is featured in the cold war thriller, "Shibumi" by Trevanian. The central character spends his adolescence studying the game under a master, and the major chapters of the book reflect Go strategies.

Shan Sa, a Chinese writer who lives in France, wrote La Joueuse de Go, where a Chinese girl plays go with a Japanese soldier and wins, although they are both extremely strong players.

Go is featured in Scarlett Thomas's book PopCo. Alice Butler, the main character, works for a giant toy company where games of Go are encouraged to spark creativity.

The world of the fantasy series The Wheel of Time has a similar game, called Stones, with a hexagonal base shape instead of square.

The book The Way of Go by Troy Anderson likens the game to a rosetta stone for understanding the underpinnings of strategy, especially for business.

In the webcomic Disassemblance, the two main characters are occasionally seen discussing various subjects over a game of Go.

The game of Go plays a part in the American TV miniseries, Wild Palms which references a piece of computer technology called a "Go chip." Go figures prominently in the introduction of Nikita to the mysterious character of Jurgen during an important character arc in the television series La Femme Nikita. The game also appeared in an episode of Star Trek: Enterprise entitled "The Cogenitor" in which it was revealed that Charles Tucker plays the game. In another Gene Roddenberry show, Andromeda, Dylan Hunt and Gaheris Rhade both play a futuristic version of the game, apparently on three boards at once. During episode 15 of season 3 of the television show 24, several scenes took place in an underground Chinese go club uncharacteristically populated by beautiful women. The characters even called it a "go club."

Hikaru no Go is a manga and anime series, in which a boy is taught to play Go by the spirit of an ancient Go player. At the end of each episode in the original anime, there is a short segment of approximately three minutes where a simple concept of Go is taught. Through the first few episodes, a new player can be taught the concepts of the game in a very simple and easy to understand format. This segment appears to be mainly geared towards children.

One popular Chinese/Japanese movie is Mikan no taikyoku (1982) aka The Go Masters. The movie depicts the time period when the Japanese army invaded China. The story begins when a Japanese Army Captain forces a famous Chinese Go player to play at a Go match. Due to resentment of the invasion, the Chinese player cuts off the finger that is used to hold Go stones. The story ends at a post-war time, where both the Japanese Captain and the Chinese Go player meet and play a peaceful game.