This study reports on findings from research carried out with Barnardo’s, a voluntary sector (not-for-profit) fostering agency, on its experience of using the Adult Attachment Interview (AAI) to assess foster carers’ attachment style. Despite growing interest in the application of standardised assessment tools to the selection and support of carers, there is currently very little research that focuses on the implementation of these tools and their added value in either an adoption or foster care setting. Research was conducted in two phases. The first phase used qualitative interviews with staff members to explore their experience of using the AAI in the early stages of its implementation. The second phase drew on qualitative interviews with staff, foster carers and fostering panel members to assess current practice 18 months later. The AAI was found to add depth and rigour to the assessment process, provided opportunities for carers to reflect on their past experiences and gave staff and carers a common language to discuss issues relating to attachment. However, the use of the AAI was not without its costs and challenges and required a significant investment of time and resources. The implications for foster care agencies are discussed.