The Pathfinder Society is a globe-spanning organization based out of Absalom, the world's largest city. The membership consists primarily of Pathfinders, adventurers who travel throughout Golarion, usually inconspicuously, and explore, delve, and otherwise experience the lesser-seen parts of the world. They send journals back to their venture-captain, who also assigns them new missions and suggests new places to explore. The most exciting and illuminating of these journals are compiled in the Pathfinder Chronicles, an ongoing series of books which collect the history and mystery of Golarion for their membership.
Factions within the Pathfinder Society are an open secret - no one discusses them publicly but everyone knows they exist. They are not formal organizations, but rather an informal alliance of like-minded Pathfinders lead by those in a position to most strongly represent their ideals.