Foster parents are often faced with serious externalizing behaviors of their foster child. These behavioral problems may induce family stress and are related to less effective parenting and often increase. Foster children with behavioral problems are also more at risk of placement breakdown. An intervention to support foster parents of young foster children with externalizing behaviors is necessary to improve the effectiveness of foster placements. Based on research on effective parenting interventions and special needs of foster children, a treatment protocol was developed. This paper describes theoretical foundations for the content and form of the intervention and gives an overview of the modular treatment protocol. Preliminary outcomes of this intervention as well as challenges and future developments and research activities are discussed.