D20 games are role-playing games that use dice with 20 sides to determine the success or failure of actions attempted by characters in the games.
D20 games were developed by Wizards of the Coast for the third edition of the Dungeon and Dragons role-playing game. Since then, many role-playing games have adopted the use of these dice. While d20 games use rolls of 20-sided dice as the basic method of determining success or failure, other dice are also used. These include dice with four, six, eight, ten and twelve sides. These other dice are often used to determine the effects of a successful roll of a 20-sided die.