Current research and observations indicate that complex processes are involved in dealing with stability and instability in family foster care. Disruptions, separations and transitions have great implications for foster children's lives, and also for the daily practice of foster families, birth parents and social workers. Against this background, the ninth International Foster Care Research Network Conference was held in September 2017 in Paris (France) on the theme 'Continuity and disruption in foster care'. A selection of the presentations there were rewritten into a paper as part of this special issue.