Domino is a game that involves the placement of small rectangular tiles, each with two groups of spots on one side. The tiles may be stacked or “stretched” out to form lines and shapes, and they are used for a variety of games. Dominoes have become a popular family pastime and are often used in schools as an educational tool to demonstrate concepts such as cause and effect. The word domino has also been incorporated into the lexicon as a figurative metaphor, meaning that one event can trigger a chain reaction that has far-reaching effects.

There are many different types of games that can be played with dominoes, but most involve some sort of strategy and a certain degree of luck. Some of the most common are block and scoring games. Blocking games involve placing one domino edge-to-edge against another to create a line that is either completely closed (no other ends touching) or forms some kind of total. Scored games generally award points based on the number of pips that show on opposing player’s tiles, and doubles may be counted as one or two (a 6-6 tile counts as six, but a double-blank counts as zero).

The most common domino sets contain 28 tiles, although larger ones exist for more players or for long domino chains. These tiles can be “extended” by adding additional pips to an end, increasing the number of possible combinations of ends. Common extended sets include double-six, double-nine, and double-18. Larger extensions exist, but are rarely used in practice.

Before a game begins, the tiles are shuffled. The player who draws the highest-valued domino goes first, or if no double is drawn, the player who has the highest-scoring hand. Once a player has their hand, they begin placing their tiles on the table. Each tile must be placed so that its matching end is adjacent to a previously-placed domino, and if it is a double, it must be crossed over a previous domino, as shown in the diagram below.

As each domino is pushed down, it generates a little bit of friction against the next tile. This tiny nudge gives the next domino the extra energy it needs to tip over, and so on. This is what makes a domino chain so effective — each domino is pushing its neighbor over and creating more momentum for the others to follow suit.