As an introduction to the special issue on attachment theory as a foundation for psychotherapy integration, this article will review the uses to which the theory has been employed by integrative theorists and clinicians during the past four decades. Reasons that this theory has been so influentially within psychotherapy integration are discussed, as are some of the models that are explicitly based on attachment theory. (PsycINFO Database Record (c) 2011 APA, all rights reserved)