His research has addressed a variety of topics related to democracy and democratization, including civil society, citizenship, hybrid regimes, right-wing extremism, and public opinion. He is the author of The Weakness of Civil Society in Post-Communist Europe (Cambridge, 2003) and Varieties of Citizenship in the European Union (Cambridge, forthcoming). He has also published articles in numerous academic journals, including the American Journal of Political Science, the British Journal of Political Science, Perspectives on Politics, the International Migration Review, and the Journal of Democracy.