Professor Fidler specializes in international law. He is one of the world's leading experts on the relationship between international law and cyberspace, cybersecurity law and policy, the rule of law in counterinsurgency and stability operations, international law and global health, biosecurity threats posed by biological weapons and bioterrorism, arms control and non-proliferation concerning weapons of mass destruction, the international legal implications of "non-lethal" weapons, and the globalization of baseball. 

In addition to his teaching and scholarly activities, Professor Fidler has served as an international legal consultant to the World Bank (on foreign investment in Palestine), the World Health Organization and the U.S. Centers for Disease Control and Prevention (on global health issues), the U.S. Department of Defense's Defense Science Board (on bioterrorism), the Scientists Working Group on Biological and Chemical Weapons of the Center for Arms Control and Non-Proliferation, U.S. Joint Forces Command (on rule of law issues in stability operations), the Interagency Afghanistan Integrated Civilian-Military Pre-Deployment Training Course organized by the Departments of Defense, State, Agriculture and the U.S. Agency for International Development, and various initiatives undertaken by non-governmental organizations in the areas of global health and arms control. 

Professor Fidler is a Fellow at the Indiana University Center for Applied Cybersecurity Research, a Fellow with the Pacific and Asia Society, and an Associate Fellow with the Centre on Global Health Security at Royal Institute of International Affairs (Chatham House). He is also a member of the Executive Committee of the American Society of International Law's Interest Group on International Law and Technology.