Implementation and compliance are two key concepts in research on the consequences of global governance arrangements generally and of the international human rights regime specifically. This chapter investigates their conceptual boundaries and distinguishes them from the related concepts of effectiveness and impact. It foregrounds the critical issue of the definition of the standards applicable to assessing (second-order) compliance and addresses the role of legal status for implementation and compliance research. Referencing the major theoretical explanations that have animated the latter, it argues that while these are often deeply entangled and overlapping, separate causal accounts for implementation and compliance are possible.