Initially, the Portuguese collection formed only a background to the collections on the wars and events in Portuguese Africa. For the Salazar and Caetano regimes, the main collecting consisted of official publications and periodicals, since political publications were discouraged. After the 1974 revolution, Hoover took advantage of the great publishing renaissance and attempted to collect as much material as possible in its traditional fields of interest.
The library holds many substantial files of several ministries and agencies responsible for colonial affairs since World War I. A series of pamphlets dealing with overseas policy, corporate organizations, labor policy, and economic development, issued for the period 1940–1945 by the Secretariado nacional da informaçáo, was acquired, as well as Portugal: Bulletin of Political, Economic and Cultural Information (1937–56), superseded by Portugal: An Information Review (1956–64 and 1970–73) from the same government office. The published works of Antonio Salazar and Marcello Caetano can be found in the library, as can the published proceedings of the trial of Henrique Galvao in 1952 and the memoirs of Humberto Delgado.
The Revolution of the Flowers of April 1974 brought about far-reaching changes in Portugal, divested it of its overseas empire, and established a democratic government in the homeland, which found itself threatened successively by the army, the Left, and the Right. Noteworthy materials for this period include the second edition of Antonio Spinola's Portugal e o futuro; the memoirs of Marcello Caetano, Depoimento; the publications of Alvaro Cunhal, the leader of the Communist Party; and the works of Mario Soares, the head of the Socialist Party.
Of particular interest is the rare file of Boletim Informativo (September 1974 - August 1975), issued by the Movimento das forças armadas. A collection of posters and ephemera in the Cornelius Drijver Collection in the archives documents the more colorful aspects of the revolution. Sound recordings of interviews with British, Portuguese, and South African diplomats, politicians, economic advisers and journalists relating to the April 1974 events can be consulted in the Robert Keith Middlemas collection.
The Institution continues to collect descriptive and analytic accounts of political events and development in Portugal.