Along with its 3.0 predecessor the Expanded Psionics Handbook is one of the most popular of the optional expansion books written for the game; expanding and adapting the psionics concept (which had appeared in all the original editions to one degree or another) with a new emphasis on balance and playability. The 3.0 version of the book mixed elements from previous versions of the game (such as Power Points from second edition) along with a number of new innovations like linking the system closer to the new system of DnD as well as balance changes such as removing the randomness that had characterized the original system. One of the key innovations was integrating the psionics system into the feats and class system that third edition emphasized. In the earlier editions most characters had a small chance to receive psionic powers as an extra set of abilities; a lucky character could receive powers that were equivalents of magical spells that were not available until mid-to-high levels. In 3.0 characters must take psionic classes or feats in order to access the abilities forcing a player to forgo other abilities in exchange for psionic powers.
The Expanded Psionics Handbook builds on the original by introducing two more new Base Classes, alters some rules and includes a new system for becoming psionically focused. Base classes in this book include the psion and psychic warrior, the wilder, and the Soulknife. There are also several prestige classes. They are the Cerebremancer, Elocater, Fist of Zuoken, Illithid Slayer, Metamind, Psion Uncarnate, Pyrokineticist, Thrallherd, and the War Mind.
The fourth edition Player's Handbook states that psionics will be a main (or core) feature rather than an expansion book.