Pathfinder is a roleplaying game based on the 3.5 edition of Dungeons & Dragons, and is sometimes nicknamed 'D&D 3.75'. It was first published in 2009 by Paizo Publishing following a mass playtest. The game is well-supported with a line of rules supplements, adventure paths, modules and scenarios. Paizo also publishes an official game setting, the world of Golarion, which is the setting for its Pathfinder Society shared-world campaign (the tabletop equivalent of an MMO).
Pathfinder makes a number of changes to the 3.5 system, aiming not only to simplify it but to make sure characters get significant improvements at every new level. Character classes have been rebalanced and skills consolidated. The procedure for performing variant combat manoeuvres has been simplified. A number of spells have been reworked.
LIke D&D3.5, Pathfinder characters are based on a class/level structure: players select a class for their character. Their action sin the game earn experience points, which earn new levels at regular experience thresholds. Charatcers may change their class on gaining a new level.
The core mechanic of Pathfinder is a twenty-sided (d20) dice roll, modified by relevant bonuses. In all cases success is determinged by equalling or exceeding a target number, thus rolling high is always desirable.
The 576-page Pathfinder Core Rulebook contains the equivalent of D&D's Player's Handbook and Dungeon Master's Guide. A series of Bestiaries provide creatures to fight.