- Norms, Ideas, and Identities: Overcoming Discrimination Against Immigrants. Princeton University Press; Princeton Studies in Political Behavior. Co-authored with Donghyun Danny Choi and Mathias Poertner. Under contract/review.
- Predicting Secession: Means, Motives and Processes. Cambridge University Press, Elements Series. Co-authored with David Siroky. Under contract (expected completion: April 2022).
- Making War and Building Peace: United Nations Peace Operations. Princeton, NJ: Princeton University Press, 2006. Co-authored with Michael Doyle.
- Understanding Civil War: Evidence and Analysis. Volume 1: Africa. Washington, DC: World Bank Publications, 2005. Co-edited with Paul Collier.
- Understanding Civil War: Evidence and Analysis. Volume 2: Europe, Central Asia, and Other Regions. Washington, DC: World Bank Publications, 2005. Co-edited with Paul Collier.
- Breaking the Conflict Trap: Civil War and Development Policy. Washington, DC: Oxford University Press and World Bank Publications, 2003. Co-authored with Paul Collier, Lani Elliott, Håvard Hegre, Anke Hoeffler, and Marta Reynal-Querol.