Online casino software enables the games to appear on the screen the way they do. The animations, graphics and sound effects that create a live casino atmosphere are the result of the software. The placing and processing of the wagers are also controlled by the software.

At the heart of the software is the Random Number Generator (RNG). All online casino games are based on random events that should be unpredictable. In roulette the outcome is a number between 0 and 36, in craps it is the total on the faces of two dice, in blackjack and video poker it is a set of cards from a standard playing cards deck and in slots it is a combination of symbols on the reels. The RNG uses complicated mathematical algorithms to generate random numbers that are fair and unpredictable. Fairness is important because each number must have equal chance of coming. These random numbers are then converted to the specific outcomes in the various games by the online casino software. In this manner the online casino software is able to simulate live gambling games. Simulating the random numbers has two advantages. They are not subject to mechanical defects and hence are fairer than in mechanical devices. The generation is done instantaneously and therefore the game speed is much faster than in live casinos.

Though simulating the casino games is the primary function of the software it is not the only one. The software has to manage and control the entire online casino operations. One of the crucial functions is the banking function. Online casinos have to accept payments from players and remit their winning when asked for. This has to be done without error and in a secure manner. Another important function of the software is to handle the bonuses offered. Online casinos offer bonuses to attract players. The casino software keeps track of when the players become eligible for bonuses, crediting the bonuses to their account and ascertaining if the wagering requirements have been met. A third major function is customer support. Players may need assistance from time to time and the software creates a mechanism for communication between players and the customer support staff.

Online casino software was developed in the mid 1990s by Microgaming and Cryptologic. Since then a number of reputed software providers have entered the market. Some of these are Playtech, Rival Gaming, Real Time Gaming, Vegas Technology and Wizards Gaming.