In most refugee situations the majority of separated and unaccompanied children are reunified with their families. However, a number of children always remain for whom tracing is unsuccessful despite extensive and comprehensive efforts. It is for these children that formal Best Interest Determination (BID) procedures are implemented to safeguard their rights and identify the most appropriate durable solution to ensure their overall well-being. This report provides some practical recommendations for the establishment and implementation of BID mechanisms for separated children, based on the BID process in Guinea for Sierra Leonean separated children.