The Division's Wildlife and Marine Resources Section is responsible for civil cases arising under the fish and wildlife conservation laws, including the Endangered Species Act, which protects endangered and threatened animals and plants, and the Marine Mammal Protection Act, which protects animals such as whales, seals and dolphins. This work includes litigation over which species should be listed as threatened or endangered under the Endangered Species Act, cases challenging the way in which protected species are considered when federal agencies carry out their missions, and other litigation related to the balance between species protection and resource development in federal agency decision-making.

The Environmental Crimes Section also brings criminal prosecutions under these laws against, for example, people who are found smuggling wildlife and plants into the United States. There is a major worldwide black market for some endangered species or products made from them. The main federal agencies that the Division represents in this area are the Fish and Wildlife Service and the National Marine Fisheries Service.