- Occupation
- Occupation
of Japan—Educational Reform in Japan, 1945–1952
- Occupation
of Japan—Framing the Constitution of Japan: Primary Sources in
- Occupation
of Japan—The Occupation of Japan
- Occupation
of Japan—The Occupation of Japan: Economic Reform,
- Occupation
of Japan—The Occupation of Japan: Economic Reform,
- Occupation
of Japan—The Rearmament of Japan
- U.S.
Occupation of Germany: Educational Reform, 1945–1949
- Oceania
- Discovery,
Conquest, and Organization of Spanish America and Oceania
- Office
- British
Documents on Foreign Affairs: Reports and Papers from the Foreign Office
- Colonial
Office Records: Class 5 Files (C.O.5)
- Confidential
British Foreign Office Political Correspondence
- Confidential
British Foreign Office Political Correspondence—Germany, Series
- Confidential
British Foreign Office Political Correspondence—Palestine and
- History
of the Office of Censorship
- Information
Control and Propaganda: Records of the Office of War Information
- Mexico:
British Foreign Office General Correspondence, 1919–1958
- Native
Americans Reference Collection: Documents Collected by The Office of
- Office
of Indian Affairs, 1824–1880: Historical Sketches
- President
Dwight D. Eisenhower's Office Files, 1953–1961
- President Franklin
D. Roosevelt’s Office Files, 1933–1945
- President
Harry S Truman's Office Files, 1945–1953
- President
John F. Kennedy's Office Files, 1961–1963
- U.S. Office of Strategic
Services, Foreign Nationalities Branch Files,
- Official Publications
- Guide
to Official Publications of Foreign Countries, 2nd Edition
- Oil
- Oil: The Federal Investigations
- Oliver
- Oliver Wendell
Holmes, Jr. Papers
- Oral
- Antitrust
Law: Major Briefs and Oral Arguments of the Supreme Court of the United
- Oral
Arguments of the US Supreme Court
- Oral Histories
- Armed
Forces Oral Histories—Korean War Studies and After-Action Reports
- Armed
Forces Oral Histories—U.S. Army Senior Officer Oral Histories
- Armed
Forces Oral Histories—World War II Combat Interviews
- Harry S Truman
Oral Histories Collection
- Oral Histories
of the Johnson Administration
- Oral History
- John F. Kennedy
Presidential Oral History Collection
- Voices
from Ellis Island: An Oral History of American Immigration
- Organizations
- American
Federation of Labor and Congress of Industrial Organizations Pamphlets,
- Oriental
- Oriental
Question, 1840–1900: Files from the Royal Archives, Windsor
- OSS
- OSS/State Department
Intelligence and Research Reports
- OSS/State
Department Intelligence and Research Reports—Africa: 1941–1961
- OSS/State Department
Intelligence and Research Reports—Asia
- OSS/State Department
Intelligence and Research Reports—Europe
- OSS/State
Department Intelligence and Research Reports—Germany and Its
- OSS/State
Department Intelligence and Research Reports—Latin America
- OSS/State
Department Intelligence and Research Reports—The Middle East
- OSS/State
Department Intelligence and Research Reports—The Soviet Union
- World War II
Research Collections—OSS/London: Special Operations Branch and
- Overland
- American
West: Overland Journeys, 1841–1880