The core of the Spanish collections consists of monographs, newspapers, periodicals, ephemera, and archival documents on the Civil War (1936–39), the latter including strong holdings on foreign participation, personal narratives, pictorial works, and regimental histories, including the International Brigades. A set of microfiches of the Blodgett pamphlet collection at Harvard complements the Hoover Institution's Burnett Bolloten papers in the archives. Additional Civil War material can be found in the papers of Bertram Wolfe and in the papers of Joaquin Maurín, the founder of the Partido Obrero de Unificación Marxista (POUM), as well as in the Mueller and Graeff photographic poster collection and on reel 19 of the Andre Marty archives.

For the Franco period, monographs, newspapers such as the Falangist Arriba (1939–74), periodicals, and opposition, separatist, and exile publications were also collected.

Collecting continued for the post-Franco period, documenting the establishment of the transition to democracy under Juan Carlos, the attempted coup against this democracy in February of 1980, entry into the European Community, and the various general elections.