From the introduction: The pass/fail dice roll is a central component of roll playing games. In the 45 years of the development of the hobby, multiple systems have come about. The purpose of this essay is to cover the basics of dice roll mechanics for multiple systems so that the reader can clearly understand how they work. Specifics of stats, attributes, skills, modifiers and conditions are intentionally avoided. Also, except where it is integral to the core mechanic, damage and criticals will not be covered. User summary: The essay specifically looks at these games/systems: d20 System Dungeons & Dragons (5th Edition) Cypher System Open Legend 2d20 System GURPS Shadowrun Savage Worlds