Michael Radu is co-chairman of the Center on Terrorism, Counter-Terrorism and Homeland Security at the Foreign Policy Research Institute in Philadelphia. He has studied terrorist groups around the world and is an expert on terrorism and extremism in Turkey.

Sandra Mackey is a freelance journalist who has written widely on Islamic extremism, especially in Iraq and Lebanon. She is the author several books on Islam and politics in the Middle East including Mirror of the Arab World: Lebanon in Conflict (2008). She lives in Atlanta, Ga.

Bruce Hoffman is a professor in the security studies program at Georgetown University in Washington, D.C. He teaches graduate courses in terrorism and counterterrorism and insurgency and counterinsurgency, as well as other international security subjects.

Tawfik Hamid describes himself as a former member of an Islamic extremist movement Jamma’a Islameia who now speaks out for political and religious reform in the Muslim world.

James Piscatori is a professor and deputy director of the Centre for Arab and Islamic Studies at the Australian National University in Canberra, Australia. He is formerly a senior scholar at the Oxford Centre for Islamic Studies in Oxford, England. He is a leading scholar in Islamic communities in the West.

Sohail Hashmi is an associate professor of international relations at Mount Holyoke College in South Hadley, Mass. He is an expert on Islam, pluralism, Islamic political thought and jihad. He posits that Islam lacks a tradition of political thought.

The Saban Center for Middle East Policy is based at the Brookings Institution, a nonprofit organization that focuses on U.S. foreign policy through funding independent research, publishing and events. It is based in Washington, D.C.

The National Democracy Institute for International Affairs is a nonprofit organization that seeks to support democracies throughout the world. Its website is searchable by some countries. Kenneth Wollack is president.

The Institute for Social Policy and Understanding is an independent nonprofit think tank committed to research and analysis of U.S. domestic and foreign policies, with an emphasis on issues related to the Muslim community in the United States. Katherine Coplen is director of communications.