This book presupposes considerable familiarity with reductive Lie groups and their lattices, as well as the elementary theory of automorphic forms. One objective of this Introduction, then, is to attempt to alleviate this burden by setting down some of the requisite facts in a precise form, giving no proofs but providing complete references. Even the expert may find it helpful to look through this material since, in so doing, he can determine what versions of the relevant definitions and theorems are going to be employed by us, there being a choice here. The other objective of this Introduction is to set the stage for the present work, i.e., to indicate its intent and scope, as well as its position in the theory taken in toto.