Abstract Background An important responsibility of the child welfare system, is taking decisions on the reunification of children with their birth parents after the children have lived in foster families. We currently lack evidence-based knowledge to guide the reunification decision-making process. Objective The present study uses concept mapping as an exploratory method, to identify themes that seem to be used by two groups of professionals in their judgement and decision making on reunification. Method First, we consulted 78 foster care workers and studied 172 legal cases to examine criteria important for reunification. Next, unique criteria were grouped and rated by 35 foster care workers and also by 12 family judges separately. The data was analysed with multidimensional scaling and cluster analysis which resulted in a concept map for each group of professionals. Results Both foster care workers and family judges suggested the following themes in the reunification decision-making process: (a) birth parents’ functioning and parenting abilities, (b) birth parents’ acceptance of support, and (c) the child’s functioning, developmental needs and wishes. Besides parallel themes, both foster care workers and family judges also seem to consider unique themes. Conclusions The suggested similarities and differences between the two groups of professionals possibly reflect different professional frameworks. The foster care workers’ considerations seem to have an orientation towards permanency planning while the family judges’ considerations seem to be linked to the legal framework. Gaining insight in the perspective of different groups of professionals involved in the process of reunification, is a small but important step towards reaching consensus through discussion in order to achieve the optimal implementation of the decisions considered in the best interest of children’s future.