A state’s good faith in the duty to cooperate in sustainable management of shared resources has a positive role in fulfilling such a duty. In interstate disputes, good faith is presumed unless there are harmful consequences from another party, but this has been challenged. Substantiating good faith enables monistic review of domestic decision making by international standards, which may raise tensions. Good faith reflects legal and extra-legal elements. The meaning of good faith in international law is ambiguous, but it has roles in creating, interpreting and performance of treaty and international obligations from other sources and so is fundamental. International judicial bodies have evaluated states' conduct by the good faith presumption, which coincides with emphasizing the difference between municipal and state law. Iinternational courts' and tribunals' review introduces a monistic approach by which bodies evaluate that in light of international standards, including hard law and soft law instruments, thereby substantializing good faith objectively and allowing review to cover states' domestic judicial, legislative and administrative conduct.