This chapter examines extant understandings of sovereignty as responsibility, beginning with the idea of sovereign responsibility as conceptualised by Francis Deng and his collaborators, who contend that sovereignty can no longer be seen as a protection against interference, but as a charge of responsibility where the state is accountable to both domestic and external constituencies. The understanding is foundational to the thinking behind the 2001 International Commission on Intervention and State Sovereignty (ICISS) report, which introduced the responsibility to protect (R2P) with the aim to popularise the concept of humanitarian intervention and democracy-restoring intervention. Since its endorsement by the United Nations, the R2P has evolved through efforts by the UN and others to enhance, operationalise as well as to implement it in actual crisis situations – with varying degrees of success and in some instances not without controversy. The chapter discusses the relevance of the sovereignty as responsibility idea to Southeast Asia. It also examines the existing academic and policy debate over the R2P and its relevance to international security and sovereign responsibility, as well as its ambivalent reception in Southeast Asia.