Encyclopedias, Almanacs, Transcripts, and Maps
- Oliver v. United States 466 U.S. 170 (1984)
- Olmstead v. United States 277 U.S. 438 (1928)
- Olney, Richard (1835–1917)
- Olsen v. Nebraska Ex Rel. Reference & Bond Association 313 U.S. 236 (1941)
- Omnibus Act 15 Stat. 73 (1868)
- Omnibus Crime Control and Safe Streets Act 92 Stat. 3795 (1968)
- On Lee v. United States 343 U.S. 737 (1952)
- One Person, One Vote
- Open Fields Doctrine
- Open Housing Laws
- Operation Liberty Shield
- Operation Magic
- Operation Shamrock
- Opinion of the Court
- Oral Argument
- Orange Volunteers (OV)
- Ordered Liberty
- Ordinance of 1784
- Oregon v. Elstad 470 U.S. 298 (1985)
- Oregon v. Mitchell 400 U.S. 112 (1970)