<P>This book is a collection of papers by leading contemporary psychoanalysts who comment on the continuing important relevance of Freud's (1911) paper, <EM>Formulations on the Two Principles of Mental Functioning</EM>. The contributors gathered here represent current European, Latin American, and North American perspectives that elaborate the continuing value of Two Principles for present-day psychoanalytic thinking. Each author examines Freud's paper through a personal lens that is coloured by the psychoanalytic culture from which he or she comes. In each instance, the writers' chapters demonstrate the heuristic value of Two Principles for twenty-first century psychoanalytic theory and technique. A common thread that runs through all the chapters is the view that this brief paper by Freud, which he humbly introduced by stating, "The deficiencies of this short paper, which is preparatory rather than expository ...", is a masterpiece that contains within it the seeds of much of his later writing. The distinction he draws between the pleasure principle and the reality principle are profound and raise questions that still preoccupy analysis today. </P>