Circle of Security Parenting (COS-P) is an attachment-theory-informed program for parents of infants and young children. Designed for scalability, COS-P has been widely adopted internationally. Evidence for the program's effectiveness is limited, however, restricting capacity to make informed decisions about program allocation, and threatening ongoing program funding. To help address this evidence gap, this qualitative study explored the experiences and perceptions of 20 COS-P facilitators and 14 parent recipients in Australia, where COS-P uptake has been particularly widespread. Thematic analysis of combined interview and focus group data revealed a perception that COS-P primarily changes the lens through which parents view (a) their child, (b) themselves in the parenting role, and (c) the parent-child relationship, and that this was a pathway to increased empathy, compassion, and parenting confidence. Participants identified four components that underpinned program impact: key content, skills practice, group processes, and facilitator support. Although COS-P was considered suitable for broad application, limitations were noted. Findings can guide clinical application of COS-P and inform empirical research.