Dominoes are small, rectangular blocks marked with two groups of spots or pips. They are used for playing various games. Like playing cards, they are often used for team or competition-oriented games. They have many different variations, with a wide variety of games and rules. Some games are even very complex, with a lot of strategy involved. In addition to their use as a game, dominoes are also commonly used for table decorations. They can be painted, engraved, or carved into various designs. Some are made from a variety of materials including marble, glass or crystal, frosted glass, ceramic clay, or metal. These sets are more expensive and are often heavier than polymer-based versions, but they have a more distinctive look and feel. While many European-style dominoes are made from bone, silver lip ocean pearl oyster shell (MOP), ivory, or a dark hardwood such as ebony, some are made from other natural materials. Occasionally, dominoes are crafted from woods such as oak and redwood or from metals such as pewter or brass. There are also variants of the game using multicolored tiles instead of single-colored ones. These can be played with up to three players. In one variant, the player who draws the last tile in a set can choose to play that same tile or to play any of the other tiles in the set. The most basic domino variant is for two players, which requires a double-six set of 28 tiles. The first player selects seven tiles from the stock. The second player then selects another domino from the boneyard that has a value equal to the values of the dominoes already selected. The pattern continues until both players have a domino of matching values or when neither player has any dominoes to play. To make the game more interesting, a few progressively larger sets have been produced, with each containing a broader range of possible end combinations and thus increasing the number of unique pieces. These are called “extended” sets, and the most common are double-nine (55 tiles), double-12 (91 tiles), double-15 (136 tiles), and double-18 (190 tiles). They are typically twice as long as they are wide. This makes it easier to re-stack the pieces. Unlike most other variants, European dominoes do not have military-civilian suit distinctions or duplicates; each piece is identified by its identity-bearing side. The game originated in China, but was introduced to Europe and eventually spread worldwide. It is believed to have been brought to England by French prisoners of war in the late 1700s. A few different theories have been proposed to explain how and why the game developed. Among them are model learning and vicarious learning. While these theories may be useful for explaining how the game works, they do not describe why it is so popular or why players continue to play it. There are other factors that may be responsible for its popularity, such as the fact that it is easy to learn and is played in a fun, social environment.