The Circle of Security (COS) Project is a 20-week, group-based, parent intervention program designed to alter the developmental pathway of at risk parents and their young children (Marvin, Cooper, Hoffman, & Powell, 2002). As the demand for early intervention intensifies, the call for effective, evidence-based, systematic treatment protocols is becoming more urgent. In response to that call, attachment theory and research have spawned an increased number of early childhood intervention programs (see Bakermans-Kranenburg, van IJzendoorn, & Juffer, 2003; Berlin, Chapter 1, this volume; Egeland, Weinfeld, Bosquet, & Cheng, 2000; and Lieberman & Zeanah, 1999, for reviews). The COS was developed to enhance relationships between young children and their parents or caregivers, what we term "attachment-caregiving relationships." To reach this goal, we integrated congruent developmental theories and object relations theory into the protocol (see, e.g., Schore, 1994). The COS was field-tested with Head Start/Early Head Start child-caregiver dyads (see, e.g., Cooper, Hoffman, Marvin, & Powell, 2000). Neil Boris and Sherry Heller at Tulane University are currently replicating the work within an experimental design; variations of the COS protocol are being implemented and tested in various sites across the country. In developing this protocol, one of our primary goals has been to incorporate advances in attachment theory and research into the actual intervention process, as well as to use attachment-based procedures for measuring outcome of the intervention. In an earlier paper (Marvin et al., 2002), we presented the general conceptual framework and a detailed description of the intervention protocol. Because the COS intervention utilizes a simple and intuitive approach to teach parents sophisticated theoretical concepts, on first view the protocol itself may appear simpler than it actually is. In this chapter, we begin with a brief description of the complex and multifaceted COS approach, and then focus on four specific principles and the COS procedures that follow from each of these principles. (PsycINFO Database Record (c) 2012 APA, all rights reserved)