The purpose of this qualitative sociological law study is to examine the relationship between the social services and civil court to apprehend if knowledge about the child's best interest is transfered from social workers to the legal system. This have been done by investigating civil court cases concerning custody transition from biological parents to foster parents according to 6 chapter 8 paragraph in the law of parenting, built upon the legal principle of the best interests of the child. Eight cases has been examined by using a method of qualitative text analysis and categorised into five primary categories and three concepts linked to sections of the law. The material has been analysed through a sociological law perspective, social constructionist theory and attachment theory. The study shows that a variety of factors interacts when it comes to determining what’s in the best interest of the child . Moreover, the civil court refers in all eight cases to social services assessments of the child's situation. This suggests that social services have an informal power position when it comes to decisions on custody transition in accordance with the child's best interests.