We have defined out of the 'depressed' category the positions that one takes to have major implications for who one treats and how, that data are going to be considered relevant, and how one organizes that data. Many of the differences in the theoretical positions taken to be discussed in this volume start with a fundamental difference in how depression is defined. We cannot pretend to resolve these controversies, but we can at least, identify them and note some of the definitions and distinctions that are being employed currently. Our purpose of this volume is to provide an overview of the phenomena of depression, as it should become apparent that there is a tremendous heterogeneity to what falls under the broad rubric of depression and it has an arbitrariness to any boundaries that are drawn on these phenomena, than others. Confronted with all of this ambiguity and confusion, one must be cautious and not seek more precision that the phenomena of depression afford, and one should probably be skeptical about any decisive statement about the nature of depression. It is also, intended to prepare the reader for the diversity of theoretical perspectives that will be presented in this volume. Contemplating the phenomena of depression, one can readily detect patterns and come to a conclusion that some aspects of depression are more central than others, some are primary and causal, and others are secondary. Cognizant of this, the observer might conclude that there is some sort of interpersonal process going on that is critical to any understanding of depression.