This final rule defines the term ``harm'', which is contained in the definition of ``take'' in the Endangered Species Act (ESA). The purpose of this rulemaking is to clarify the type of actions that may result in a take of a listed species under the ESA. This final rule is not a change in existing law. It provides clear notification to the public that habitat modification or degradation may harm listed species and, therefore, constitutes a take under the ESA as well as ensuring consistency between NMFS and the Fish and Wildlife Service (FWS). This final rule defines the term ``harm'' to include any act which actually kills or injures fish or wildlife, and emphasizes that such acts may include significant habitat modification or degradation that significantly impairs essential behavioral patterns of fish or wildlife.