The Responsibility to Protect doctrine (R2P), now ten years old, has been widely accepted at the international level. As the books under review demonstrate, debates around its legitimacy are over. Instead, we see a developing second generation of literature focusing on how the R2P needs to be understood more concretely in both academic and policy terms, as well as how it affects the linked issues of humanitarian intervention and state-building. Within this literature, we see new and important questions emerging. These include how and when we should intervene and whether we can be successful at it; how we can assist states to ensure they fulfill their own responsibilities towards their populations; and where international authority lies. Unfortunately, the answers to these questions are hard ones. Implementation, and how it reflects embedded culture at the international level, may be as hard—if not harder—as introducing the doctrine originally.