Scrabble is a word game in which two to four players score points by placing tiles bearing a single letter onto a board divided into a 15×15 grid of squares. The tiles must form words that, in crossword fashion, read left to right in rows or downward in columns, and be included in a standard dictionary or lexicon. The game is sold in 121 countries and is available in 29 languages; approximately 150 million sets have been sold worldwide and roughly one-third of American and half of British homes have a Scrabble set.
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In 1938, American architect Alfred Mosher Butts created the game as a variation on an earlier word game he invented called Lexiko. The two games had the same set of letter tiles, whose distributions and point values Butts worked out by performing a frequency analysis of letters from various sources, including The New York Times. The new game, which he called "Criss-Crosswords," added the 15×15 gameboard and the crossword-style game play. He manufactured a few sets himself, but was not successful in selling the game to any major game manufacturers of the day.
There are numerous variations of the game. While they are similar to the original Scrabble game, they include minor variations. For example, Literati draws random tiles instead of providing a finite number of tiles for the game, assigns different point levels to each letter and has a slightly different board layout, whereas Lexulous assigns eight letters to each player instead of seven. Words with Friends uses a different board layout and different letter values, as does Words of Gold.
A duplicate Scrabble tournament in La Bresse, France Duplicate Scrabble is a popular variant in French speaking countries. Every player has the same letters on the same board and the players must submit a paper slip at the end of the allotted time (usually 3 minutes) with the highest scoring word they have found. This is the format used for the French World Scrabble Championships but it is also used in Romanian and Dutch. There is no limit to the number of players that can be involved in one game, and at Vichy in 1998 there were 1485 players, a record for French Scrabble tournaments.
Scarabeo is a variant that is much more popular in Italy than the original game. It features a 17×17 grid of cells and peculiar rules.
Nowadays, the name is a trademark of Hasbro, Inc. in the United States and Canada; outside these two countries it is a trademark of Mattel.
Source and more info: Wikipedia.
What's it worth? Take a look at this Scrabble price guide: sold listings for a value indication.