Inter-municipal cooperation is gaining in popularity in many Western countries, making it a matter of pressing importance to better understand what factors might contribute to the success of such arrangements. This article focuses on three Norwegian inter-municipal cooperative arrangements in the field of child welfare that are deemed to be successful, and the aim is to identify common features across the three cases with a focus on the governance structures of the collaborations. The study combines document studies and qualitative interviews, and reveals three main factors that can explain success: a sense of urgency, political and administrative support combined with incremental processes. The study also indicates that these factors interact, and can thus not be viewed as explanations taken individually. Furthermore, the potential negative effects on allocative efficiency are highlighted. Since the success of inter-municipal cooperation seems at least partly to depend on whether the task in focus is “moved out” of the ordinary activity and embed- ded in a higher political and administrative level, it is argued that this may further frag- ment the municipalities’ ability to make priorities between sectors and services.