Ensuring the stability of foster placements for looked after children is a priority for social services. Many previous studies have highlighted the negative psychological, social and academic consequences of placement breakdown for foster children, but less is known about how services can effectively promote placement stability. A systematic review and narrative synthesis of research examining correlates of placement moves and breakdown were undertaken in order to inform practice in this area. Qualitative studies were included alongside quantitative research, providing additional insights into the processes that facilitate and impede placement stability. Correlates of increased placement instability with the strongest evidence included older age of children, externalising behaviour, longer total time in care, residential care as first placement setting, separation from siblings, foster-care versus kinship care and experience of multiple social workers. Key protective factors included placements with siblings, placements with older foster-carers, more experienced foster-carers with strong parenting skills, and placements where foster-carers provide opportunities for children to develop intellectually. Following from these findings, a conceptual framework is proposed that distinguishes vulnerability and protective factors as well as background and immediate factors. Implications for front line social work practice, including the development of manualised tools, are discussed.