Planetary and legal boundaries can only be effective if they are observed, respected and complied with. In Chapter 10, Jonas Ebbesson addresses the critical issue of compliance with planetary boundaries in international law. He shows that although the planetary boundaries have no formal status in international law, they are legally relevant. Therefore, if they obtained a more robust status in international law, though planetary boundaries would not per se create legal standards, and it would still be problematic to hold States’ performance or compliance directly against them; they would amount to objectives to be achieved and operationalised through other norms, whether rules set out in treaty law with examinable criteria for compliance, or principles of customary law. Alternatively, the planetary boundaries could influence legal concepts, principles and obligations more subtly through jurisprudence and doctrine. The chapter shows that compliance with international environmental law involves a broad range of considerations, including practical reasons for failure to comply, the legal implications of non-compliance, the institutional procedures for compliance control, and the effectiveness of compliance reviews. The main concern in this respect is whether the planetary boundaries as such can be complied with in the first place, and if not, how can compliance in relation to planetary boundaries be meaningfully examined in legal terms?