Dominoes are rectangular pieces of plastic or wood bearing a series of dots on one side and blank or identically patterned on the other. The identifier on each side is called a pip, and the total number of dots or pips on a domino determines its value in most games played with them. Unlike playing cards, dominoes are normally twice as long as they are wide and may be set on edge to make them easier to stand up and play. Dominoes are used in a variety of games, and they serve as a popular classroom activity for teaching the commutative property of addition and the number system.

In the most basic of domino games, each player in turn places a domino edge to edge against another so that the adjacent faces are either identical or form some specified total (e.g., five to five). A domino may also be positioned so that its exposed ends match (one’s touching one’s, two’s touching two’s, etc.) or, as is sometimes done in certain positional games, so that all of the dots on a given tile are exposed and countable.

The most common game of domino uses a double-six set of 28 tiles. These are shuffled and then formed into a large pile, called the stock or boneyard, from which each player draws seven tiles, to be placed on-edge in front of him.

After a player has drawn his seven tiles, he begins play according to the rules of the particular game being played. A player may open his hand by playing a single tile or, as described below, he may bye a domino from the stock by passing it to another player without revealing its value.

Most dominoes are played on a table, although they may also be used on other surfaces, such as a floor. A hard surface is preferred because it makes it easier to stand the tiles on-edge in front of a player.

Players must be sure that their tiles are matched correctly before making a play, or they will not score. The most commonly used matching rule is to have the heaviest tile begin play, with the heaviest being the top of the pile. Other rules, such as counting the pips on the exposed ends of a tile to determine its value, are employed in some games.

In the case of a chain, each domino must be played so that its two matching ends touch (one’s touching one’s, or two’s touching two’s) or, as is often done with doubles, so that one end is at right angles to the other, which will then form a snake-like line. Some chains have a single starting point, such as a heaviest double or the top of the pile, while others have no specific start, with each player simply choosing to place the first tile to begin the chain.