Steven Ratner's teaching and research focus on public international law and on a range of challenges facing governments and international institutions since the Cold War, including territorial disputes, counter-terrorism strategies, ethnic conflict, state and corporate duties regarding foreign investment, and accountability for human rights violations. Professor Ratner is also interested in the intersection of international law and moral philosophy and other theoretical issues. A member of the board of editors of the American Journal of International Law from 1998 to 2008, he began his legal career as an attorney-adviser in the Office of the Legal Adviser at the U.S. State Department. He has since advised governments, international organizations, NGOs, and corporations on a range of international law issues.  Since 2009, he has served on the State Department's Advisory Committee on International Law and since 2013, he has been an adviser to the American Law Institute for the Restatement (Fourth) of the Foreign Relations Law of the United States. In 2010–2011, he was a member of the UN's three-person Panel of Experts on Accountability in Sri Lanka.  He has also served as an expert on international investment law in various arbitrations.  He is a member of the American Law Institute.

International law Foreign investment International human rights International humanitarian law United Nations and international organizations