Carolyn Gallaher does research in two areas. Her first area focuses on organized violence by non-state actors, including militias, paramilitaries, private military contractors, and drug cartels. She published her first book on the US Militia Movement (On the Fault Line: Race, Class, and the American Patriot Movement, Rowman and Littlefield 2003) and her second book on Loyalist Paramilitaries in Northern Ireland (After the Peace: Loyalist Paramilitaries in Post-accord Northern Ireland, Cornell 2007). Her second stream of research focuses on gentrification in the DC metro area. In 2016 she published a book on how tenants resist gentrification during DC's real estate boom in the early 2000s (The Politics of Staying Put: Tenant Right-to-Buy in Washington DC, Temple 2016).