Editing Dungeons & Dragons 3rd Edition (section)

===The Core Mechanic===
3rd edition introduced the now ubiquitous "[[d20 System]]", where almost every action with a chance of failure is resolved by rolling a d20, applying relevant modifiers, and comparing the result to a set difficulty (or, in some cases, another character's roll) to determine success, referred to by the system as the "Core Mechanic". For example, a fighter attempting to hit a monster with his sword rolls a d20 and may add his Base Attack Bonus, Strength bonus, relevant Weapon Focus boni, magical enhancements, etc. with the objective of beating his opponent's Armor Class. Rolling equal to or over the target's AC means he has successfully hit and gets to deal damage. In a similar vein, a rogue attempting to pick a lock rolls a d20 and adds his skill ranks, dexterity bonus, any relevant skill boni from feats, modifiers depending on the quality of his equipment, etc. in an attempt to beat the target DC (Difficulty Class) of the lock.

This was generally regarded as a significant improvement on the systems used in 1e and 2e, where many different parts of the game were governed by vastly different mechanics. Restructuring the game around the single core mechanic made gameplay much simpler and easier to pick up for new players.