Abstract This chapter examines failures by outside actors to protect populations from mass atrocities such as genocide and crimes against humanity. It begins by tracing the origins of ‘failures to protect critiques’, whereby many observers express moral outrage against bystander states which they believe should have done more. In this discourse, mass atrocities are attributed to a combination of acts by perpetrators and omissions by bystanders. The chapter analyses the legal basis for applying the ‘failure to protect critique’ to both perpetrators and bystanders. In particular, it discusses the extent to which international law allows holding individual bystander states responsible for a failure to protect. It also discusses the failure to protect-critique on the United Nations and other international organizations. The chapter suggests that international law justifies and even requires inaction among bystander states and international organizations when mass atrocities occur.