Samuels specializes in comparative politics. He is the author of Ambition, Federalism, and Legislative Politics in Brazil (Cambridge University Press, 2003), and has published articles in many of the field's top journals. In addition to Brazilian politics, he has also published articles on political institutions in Middle Eastern countries. These works, including "Separation of Powers" in the Oxford Handbook of Comparative Politics, are considered by many scientists to be an important contribution to Middle Eastern political science.