- Obscenity
- O'Connor v. Donaldson
- O'Connor v. Ortega
- O'Hare Truck Service, Inc. v. City of Northlake
- Ohio Adult Parole Authority v. Woodard
- Ohio v. Robinette
- Olmstead v. United States
- Oncale v. Sundowner Offshore Services Incorporated et al.
- Oregon v. Elstad
- Oregon v. Mathiason
- Oregon v. Mitchell
- Oregon v. Rideout
- Ornelas v. United States
- Orr v. Orr
- Orzoco v. Texas
- Osborne v. Ohio
