Few evidence-based methods for case management in child protection and child welfare are available. That is why Youth Protection Amsterdam Area developed a new method, by integrating their best practices: Intensive Family Case Management (IFCM). Because IFCM was developed in practice, clarity about its core elements and behavior acts was lacking. The purpose of this study was to establish a valid operationalization of IFCM used for implementation purposes such as training, clinical supervision and monitoring. A 74-item draft was developed to describe the behavioral acts of IFCM, based on a literature study and analysis of internal documents and training. To ensure content validity, a Delphi study was conducted. Over two rounds, professionals (1) rated the behavioral acts needed in the application of IFCM on a five-point Likert scale and (2) provided their preferred terminology. Items with consensus ratings of 80 % or more were included in the final description. Selected IFCM experts rated the behavior acts over two rounds. The initial list with 74 behavior acts was reduced to 55 acts with a consensus of 80 % or more. Certain behavior acts were combined, others did not lead to consensus. Based on experts’ feedback, the initial terminology of 46 behavior acts was modified. The final 55 acts were categorized in ten core elements. This study explicates the core elements of IFCM and describes the 55 necessary behavior acts in preferred and recognizable terminology. The study describes implications of these findings for the practice and gives recommendations for future research.