This article describes the Circle of Security-Classroom (COS-C) approach to applying attachment theory in preschool settings. Early childhood is an incubator for a wide range of development including the underpinnings of school readiness. Secure teacher-child relationships support this process. However, most preschool staff members lack guidance in cultivating secure attachments with students. COS-C can meet the need for this specialized skill. The authors describe the principles of COS and explain the COS-C approach. COS-C is designed to enhance teachers' abilities to form secure relationships, overcome obstacles in children's abilities to engage in secure attachment, and create classrooms that promote security.