Like the polarized mix of extravagant praise and merciless scorn that greeted it from the outset, the first decade of the Responsibility to Protect (R2P) has been anything but neutral. The highs have been remarkably high, the lows painfully low. R2P has gained far broader and more sustainable political support than skeptics would have imagined, but its achievements on the ground--in preventing mass atrocities and protecting populations--have fallen far short of its proponents' ambitions. Its successes have been quiet, and its failures raw and public. Now, the task is to reposition R2P to meet changing conditions and to reflect lessons learned without losing its enduring core principles, which remain every bit as compelling today as a decade ago. The world has gotten a lot rougher since heads of state and government gathered for the World Summit in September 2005 and, to almost everyone's surprise, endorsed R2P by consensus. Long-suppressed geopolitical contradictions among the big powers have surfaced, environmental and resource pressures have sharpened, and nonstate armed groups with vicious sectarian agendas have emerged to challenge the existing normative order by flouting human rights and human protection norms on a daily basis. According to the UN High Commissioner for Refugees (UNHCR), the ranks of forcibly displaced persons reached a new peak of almost 60 million at the end of 2014. R2P did not cause any of this, but these worrisome trends underscore the need for a sober assessment of its record to date and for a fresh look at how early assumptions have withstood the test of time. Experience has reaffirmed the wisdom of the summit text in at least three respects. First, the summit cast R2P in sufficiently broad terms to permit substantial adjustments as circumstances and practice demanded. That amendment process is already well under way. In designing the Secretary-General's three-pillar implementation strategy, it was evident even in 2008 that the protection principles adopted by the summit had to be extended to nonstate armed groups. There already had been several situations in which governments had failed to exercise effective control over all of their territory so that armed groups had committed mass rapes, mutilations, and murders. The Secretary-General and I understood that international engagement should be early and flexible, depending on the circumstances of each case, and not dependent on Security Council authorization when undertaken under Chapter VI or VIII of the UN Charter. Within those bounds, the Secretariat did not need to get the permission of the five permanent members to take preventive action in Kenya, Kyrgyzstan, Guinea, Cote d'Ivoire, and other places. Our efforts to convince leaders in countries under stress to take a different path did not always succeed, but we were acutely aware that personal diplomacy, often with regional partners, and the bully pulpit were unique assets of the Secretary-General and his representatives. Our responsibility was twofold: to make the members of the Security Council and other key actors aware of the risks of atrocity crimes and to be the voice of the vulnerable even when great-power politics did not permit more forceful action. And we learned in Sri Lanka the high cost of failing to be sufficiently outspoken. Second, for all of its ups and downs in practice, in political and normative terms the progress of R2P has been remarkably rapid, especially compared to other human rights and human protection norms. Among the member states, there are still questions about implementation--as well there should be--but not about the validity and legitimacy of the prevention and protection principles that lie at the heart of R2P. The level of understanding, not just acceptance, today is much deeper and much wider than when I crafted the Secretary-General's initial statements and report seven years ago. We turned what most observers claimed was the Achilles' heel of the summit agreement--the General Assembly's continuing consideration--into a series of annual reports and Assembly dialogues on different aspects of R2P that have sharpened doctrine and advanced acceptance of the norm. …