This book examines the hard legal core, if any, of the "Responsibility to Protect (R2P)" concept with regard to the commitment to take collective action through the UN Security Council. It addresses the question of whether public international law establishes a duty on the part of the individual Security Council members to collectively take the necessary action to prevent atrocities (genocide, crimes against humanity, war crimes and ethnic cleansing). To this end, it offers an interpretation of provisions in multilateral conventions, such as the undertaking to prevent genocide in Article 1 of the Genocide Convention and the undertaking to ensure respect for the Geneva Conventions in common Article 1 of the 1949 Geneva Conventions, analyses the UN Charter framework for Security Council action, and explores whether the recognition of the international responsibility to protect has prompted the emergence of a new norm for general international law.