Andrew C. Mergen is deputy section chief in the appellate section of the Environment and Natural Resources Division at the U.S. Department of Justice, where he supervises a wide variety of litigation.

He has presented oral arguments in all 13 federal courts of appeals and several state intermediate and supreme courts. Professor Mergen also has taught at several law schools including, most recently, Harvard Law School.

Professor Mergen has written about federal water rights in "A Misplaced Sensitivity: The Draft Opinions in Wyoming v. United States" (68 Colo. L. Rev. 683 (1997), with Sylvia F. Liu); energy development on public lands in "Surface Tension: The Problem of Federal Private Split Estates" (33 Land & Water L. Rev. 419 (1998)); and, more recently, climate change and the Endangered Species Act in "The Role of Climate Change in ESA Listing Decisions" (53 Rocky Mt. Min. L. Fdn. 67 (2016), with Murray Feldman).