Encyclopedias, Almanacs, Transcripts, and Maps
- Organized Crime Control Act 84 Stat. 922 (1970)
- Original Intent
- Original Jurisdiction
- Original Package Doctrine
- Originalism
- Orozco v. Texas 394 U.S. 324 (1969)
- Osborn v. Bank of the United States 9 Wheaton 738 (1824)
- Otis, James, Jr. (1725–1783)
- Overbreadth
- Overruling
- Overt Acts Test
- Owen v. City of Independence 445 U.S. 622 (1980)
- Oyama v. California 332 U.S. 633 (1948)
- P-3 Orion Anti-Submarine Maritime Reconnaissance Aircraft
- Pace v. Alabama 106 U.S. 583 (1883)
- Pacific Northwest National Laboratory
- Packers & Stockyards Act 42 Stat. 159 (1921)
- Paine, Thomas (1737–1809)
- Pakistan, Intelligence and Security
- Palestine Liberation Front (PLF)