The Storyteller's Codex is a core book needed by the Storyteller (Game Master) in order to run a game. It has everything in it the Players should not know... Greater, Original, and Wild magic systems, Personalities and Fey, NPC Fighting Arts, poisons, Artifacts, all from a Storyteller's perspective.
The Adventurer's Rulebook is a core book needed by the Storyteller and each Player. It has everything in it the Players should know to bring a character to greatness. Character creation, Skills, 8 Fighting Arts, 100s of Traits/Flaws, 100s of Talents, Open Magic, Combat, Callings, Vocations, etc.