O'Brien
- Belron
- Brien
- Capitan O'Brien-class submarine (1928)
- Chilean submarine O'Brien (S22)
- Justice O'Brien (disambiguation)
- O'Brian
- O'Brien (Nineteen Eighty-Four)
- O'Brien (TV series)
- O'Brien (surname)
- O'Brien County, Iowa
- O'Brien Island
- O'Brien Island, Chile
- O'Brien dynasty
- O'Brien, Argentina
- O'Brien, California
- O'Brien, Florida
- O'Brien, Oregon
- O'Brien, Texas
- O'Brien, West Virginia
- O'Briens Hill, Queensland
- O'Briens Irish Sandwich Bars
- O'Bryan
- Oberon-class submarine
- USS O'Brien
- United States v. O'Brien