It’s a D&D Rules Supplement book by Mike Mearls, Rob Heinsoo, and Robert J. Schwalb, contains rules for psionic, divine, and primal heroes.

Player’s Handbook 3 expands the range of options available to D&D players with new classes, races, powers, and other material.

This book builds on the array of classes and races presented in the Player’s Handbook and Player’s Handbook 2 core rulebooks, presenting old favorites and new, never-before-seen options to the game. Player’s Handbook 3 also adds the psionic power source to the 4th Edition D&D game, along with several new classes that harness this power source.