Julius Ruiz has written widely on the Spanish Civil War and the Franco regime. His first book, Franco's Justice: Repression in Madrid after the Spanish Civil War, was published in 2005 and in Spanish translation in 2012. His second book, El terror rojo: Madrid 1936, was published in 2012 and is currently in its third printing. It won the 2012 Hislibris Prize for the best non-fiction title published in Spain and was widely reviewed in the Spanish press. Ruiz has published articles in British, American, and Spanish journals such as Contemporary European History, the Journal of Contemporary History, and Historía y Política. He has reviewed books for a large number of titles, including English Historical Review and La Revista de Libros. He is a member of the British Royal Historical Society.