Editors' Summary: CERCLA and the Oil Pollution Act (OPA) create causes of action for damages to natural resources—for damages "resulting from" a release or threatened release of a hazardous substance, in the case of CERCLA, and for damages that "result from" a discharge or threatened discharge of oil in the case of the OPA. Thus, natural resource damages actions under these acts require a causal link between the release or discharge and the natural resource damage at issue. This Article traces the development of this causal link—from early judicial opinions to recent agency regulations. The Article analyzes how the federal natural resource trustees, DOI and NOAA, have incorporated the causal link requirement into their natural resource damages assessment regulations. The Article concludes by highlighting causation issues that may permeate any assessment or subsequent litigation.