Everyone familiar with Rahner's great 23-volume Theological Investigations knows the series is hard to use because it lacks a key. The titles often fail to describe the contents of the essays accurately; there is no cumulative index in English; the existing indices at the end of each volume are tedious and failed to distinguish significant discussions of a topic from casual references; and short of wading through an entire essay there is no way to know quickly whether it contains the material one is looking for. This book attempts to address these problems.