Slot machines accept money either by cash or paper tickets with barcodes. When the coin is inserted, the machine spins the reels and awards credits to the player if certain symbols appear on the winning combination. The symbols differ from game to game, but classic symbols include bells, fruit and stylized lucky sevens. Most slot machines also feature bonus features, which are often aligned with the theme of the game.

The first fully electromechanical slot machine was produced by Bally in 1963. Earlier, the company developed a draw-poker machine known as the High Hand. Its bottomless hopper allowed for automatic payout of up to 500 coins. Its popularity led to the increased use of electronic games. The side lever, which was once an important part of slot machine design, became a vestigial part of the machine.

Some states have banned slot machines completely, and others have imposed restrictions that limit how many machines can be sold. However, in most states, private ownership is still allowed. In Nevada, there is no legal limit on the number of slots a private individual can own. In Indiana, slot machines are allowed on riverboats. In Louisiana and Mississippi, slot clubs are permitted only in specially licensed gambling zones.

Some of the earliest slot machines had little or no payout. These machines are known as pachisuro or pachislot and are a descendant of the popular Japanese pachinko game. Slot machines are relatively new in Japan and can be found in pachinko parlors and adult sections of arcades, called game centers.