Roullete, also known as roulette, is a gambling game in which a small ball is released into a spinning revolving wheel and players make wagers on the number or grouping of numbers that the ball will enter when it comes to rest. Bets can be made on a single number, various groups of numbers, red or black, odd or even, whether the number is high or low, and so on. The payouts for winning bets are based on the number of chips that form part of the specific bet.

The roulette wheel consists of a solid wooden disk slightly convex in shape, with a metal separators around its rim that create pockets that are painted alternately red and black, and numbered nonconsecutively from 1 to 36. A 37th compartment is green and carries the sign 0; on American wheels there are two additional green compartments, one on each side of the zero. The numbers are grouped into three columns and twelve rows; bets placed on six of the thirteen numbers (the second dozen) pay out at odds of 2-1.

The ball is a small, light sphere, usually made of ivory although today most professional balls are made of synthetic materials that resemble ivory. The dimensions, weight, and material of the ball have a significant impact on how well or poorly a system for playing roulette performs. A smaller, lighter ball makes more revolutions on the wheel track and jumps more unpredictably before coming to rest than a large, heavier ivorine ball. In addition, the symmetries of the roulette wheel and betting table can be exploited by mathematical systems for beating roulette. However, despite these advantages, no betting system can transform a subfair game into a profitable enterprise. The casinos, of course, know this. They won’t call “no more bets” before the ball is in motion; doing so would cut into profits and deter casual gamblers.