While some casino games have a skill element within the outcome, some casino games are purely based upon chance. Because all lottery online casino games are partly or completely driven by chance, all casino games depend on a random number generator, or RNG in the software that powers the game. The RNG is a mathematical application that does just what it says: generates a totally random number. Not all RNGs are identical, and they have to be tested extensively to ensure that the numbers they generate really are random.

In some games, the usage of an RNG has an obvious role. In European roulette, by way of example, the RNG generates a number from 1 to 37 (with 37 corresponding to "0") on the roulette wheel. The RNG generates a number, the casino stops, and bets are paid or forfeited.