This book ambitiously weaves together history and politics to explain all of the major situations where mass atrocities have occurred, or been prevented, over the 15 years since the 'Responsibility to Protect' (R2P) was adopted at the 2005 UN World Summit. The author provides a history of human rights, mass atrocities and the principle of the R2P from the perspective of someone whose day job has been to work with the UN Security Council, various governments and civil society to help ensure the international community does not fail those who face the threat of genocide, war crimes and crimes against humanity today. It examines the implementation of the controversial principle of R2P since 2011 and how we end the politics of impunity, indifference and inaction once and for all. Using case studies from Iraq, Syria, Myanmar and Libya, the book offers a unique perspective regarding how we make 'never again' a living principle, rather than a cliché and how we end the politics of impunity, indifference and inaction once and for all. It will be of especial interest to scholars, students and policymakers working in the fields of international politics or concerned about human rights, atrocities, the United Nations and international justice in the world today.