For over fifty years we have studied destructive and self-destructive sadomasochistic behavior in individuals, from failure-to-thrive infants to uncontrolled violence in children, to murder and suicide in adolescents and adults. In ordinary clinical work, all the patients we see present with some degree of sadomasochistic functioning, no matter what the diagnosis. Repetitive, resistant, self-defeating functioning, stalling or impasse in the clinical relationship - these form the arena for most analytic endeavors. In our writings on these topics, we have particularly highlighted traumatic origins, helplessness, overwhelming rage, the impact of preoedipal, oedipal, and post-oedipal pathology, terror of affects and excitement, tyrannical superego, and the constant danger of self-destruction. In this book we hope to present in summary form the basic ideas that have emerged from this work. Rather than detail the arguments, rationales, and underpinnings here, we will direct the reader to those in various other, more extensive discussions. Here we will bring into one place statements and descriptions of how our model of two systems of self-regulation has worked for us to generate a fruitful perspective on development and clinical technique. Part I of the book will take us through developmental phases from pregnancy to old age. In Part II we will turn to descriptions of how our two-systems model can inform and enhance clinical technique in therapies of various kinds.