Costenbader's expertise is in social and environmental law and policy, with 20 years of experience in the U.S., Latin America, Africa, Southeast Asia, Europe and the Pacific . Currently at the United States Department of Interior, Costenbader provides legal advice on environmental, natural resources and property issues to the Bureau of Indian Affairs. Previously, as Costenbader advised clients  and field programs on climate change, forestry/REDD+, renewable energy and energy efficiency, natural resources management, biodiversity 

conservation, agriculture systems, and land use-related legislation, regulations, policies, and social and environmental safeguards. Costenbader's focus included working with Indigenous Peoples in the 

Amazonian regions of Brazil, Peru and Colombia.  In 2009, Costenbader edited the volume IUCN Legal Frameworks for REDD – Design and Implementation at the National Level. IUCN, Gland, Switzerland, the volume is a compilation of findings of national case studies addressing the stages of REDD preparedness.

Costenbader has a Juris Doctor from The George Washington University Law School, Master of Public Affairs in Environmental Policy and Natural Resource Management from Indiana University School of Public and Environmental Affairs, and Bachelor in Philosophy from Colby College in Maine. Costenbader is a member of the New York Bar and the District of Columbia Bar Association.