Domino is a small rectangular wood or plastic block with a face marked with dots resembling those on dice. It can be stacked on one another in different configurations to form structures, such as straight or curved lines, grids that form pictures when they fall, or 3D towers and pyramids. There are many games played with dominoes, but all of them involve the same basic concept: a single domino, if tipped ever-so-slightly, causes a chain reaction that causes all the others to fall. The phenomenon is similar to how a firing neuron sends a pulse that triggers all the others in the line of cells it travels through.

The most popular domino games fit into four categories: bidding, blocking, scoring and round games. Some games are played with just a few dominoes, while others require a large number. Typically, the player who has the highest double or the heaviest single begins play. A tie can be broken by drawing new hands, as described in the rules of the game being played.

Most domino sets are made of polymer, which allows them to be very durable and colorful. In the past, however, dominoes were also made of bone, silver lip ocean pearl oyster shell (mother of pearl), ivory and a dark hardwood such as ebony, with white or black inlaid pips. Such sets are often more expensive, but they have a more distinctive look.

In many domino games, a line of tiles is formed by matching the pips on the open ends of each tile. This is called the line of play. A player makes a play by placing a domino in the line of play that matches the open end of a domino in his hand or on the edge of the table. He may draw the number of tiles he is allowed to take from the stock, as described in the rules of the specific game being played.

If a player draws more dominoes for his hand than he is permitted to, it is known as an overdraw. He must then return the extra tiles to the stock and reshuffle the deck before anyone else draws them. If the player cannot make a play with the tiles he has in his hand, he must draw a new set of dominoes from the stock to begin play.

Most domino games are played by two or more players. To determine which player will make the first play, players usually draw lots or follow the rules of the specific game being played. Some games allow players to make the first play if they hold the highest double or the heaviest piece, while others stipulate that the winner of the last game begins play. If no player can make a play, the game ends.