A man named Charles Fey developed the first commercially successful slot machine in his San Francisco machine shop around 1896. Made of cast iron with three internal reels, a slot for taking in coins and an external lever for activating the machine, it quickly became a staple of saloons, gambling houses and even many retail stores (where patrons would trade their winnings for goods from the store – hence the term "trade goods").

Today, no casino would be complete without gleaming rows of noisy, colorful, brightly lit slot machines. The mix of sounds from hundreds of machines chirping, spinning, stopping and clinking out coins is the iconic background music that fills every casino floor. They are by far the most popular casino game in the world, both in terms of number of games played and total wagers.

With the advent of digital electronics, slot machines have expanded from the original mechanical design to a wide range of computer-generated displays with multi-stage games and other new twists on an old favorite. First came multi-line slots with additional pay lines. Then video slots came on the scene to give game designers much more freedom to create interesting and innovative variations. Because they are computer-based, a number of video slots can be linked together to establish rapidly growing progressive jackpots.

With this continual evolution in excitement and entertainment value, the Slot Machine will remain as the most popular casino game for years to come.