A threshold question for designing liability rules is the degree of fault required to impose liability. This chapter begins with a discussion of the policy considerations that underlie the policy choice between strict liability and due diligence approaches to liability and an examination of the distributive implications of this choice. The chapter then describes the approaches to standards of liability found in the law of state responsibility and civil liability regimes, before examining the specific fault requirements that structure liability in the Antarctic, deep seabed and high seas regimes.