The Responsibility to Protect (R2P) is an example of "responsibility" becoming an institutionalized part of normative order, not only in practice but also in name. This chapter asks how the introduction of responsibility contributed to negotiating the protection of populations from war crimes, crimes against humanity, genocide, and ethnic cleansing and what we can learn about responsibility in world politics through the case of R2P. The chapter starts with the protection dilemmas that arose by the end of the 1990s and shows that introducing responsibility to the debate responded to these normative conundrums on four levels: of discourse, institutionalization, collective expectations, and public justifications for state action. It argues that, on all four levels, responsibility facilitated the negotiation of protection, i.e. led to a better specification of what protection is and who should carry it out. It did so by providing politically acceptable terms of debate on the level of discourse and facilitating institutionalized knowledge on mass atrocities in policy-making. On the levels of collective expectations and public justifications for action, it ignited debates on specific responsibilities and understandings of protection, thus clarifying expectations on how to protect.