A full set of Go stones (goishi) usually contains 181 black stones and 180 white ones; a 19?19 grid has 361 points, so there are enough stones to cover the board, and Black gets the extra odd stone because that player goes first. There are two main types of stones: single-convex, in which one side is flat, and double-convex, in which both sides have a similar curve. Each type has its pros and cons: single-convex stones, placed flat side down, are less prone to move out of position if the board is bumped or disturbed by nearby movement. In addition, during post-game analysis, players can try out variations using upside-down stones, making it easy to remember the actual game moves. On the other hand, flat stones are harder to clear from the board at the end of the game.

Traditional Japanese stones are double-convex, and made of clamshell (white) and slate (black).? The classic slate is nachiguro stone mined in Wakayama Prefecture and the clamshell from the Hamaguri clam; however, due to a scarcity in the Japanese supply of this clam, the stones are most often made of shells harvested from Mexico. Historically, the most prized stones were made of jade, often given to the reigning emperor as a gift.

In China, the game is traditionally played with single-convex stones made of a composite called Yunzi. The material comes from Yunnan Province and is made by sintering a proprietary and trade-secret mixture of mineral compounds. This process dates to the Tang Dynasty and, after the knowledge was lost in the 1920s during the Chinese Civil War, was rediscovered in the 1960s by the now state-run Yunzi company. The material is praised for its colors, its pleasing sound as compared to glass or to synthetics such as melamine, and its lower cost as opposed to other materials such as slate/shell. The term "yunzi" can also refer to a single-convex stone made of any material; however, most English-language Go suppliers will specify Yunzi as a material and single-convex as a shape to avoid confusion, as stones made of Yunzi are also available in double-convex while synthetic stones can be either shape.

Traditional stones are made so that black stones are slightly larger in diameter than white; this is to compensate for the optical illusion created by contrasting colors that would make equal-sized white stones appear larger on the board than black stones.