Encyclopedias, Almanacs, Transcripts, and Maps
- Ofner, Julius
- Ofran
- Og
- Ogilvie, John, St.
- Ohel
- Ohev ben Meir Ha-Nasi
- Ohio, Catholic Church in
- Oholiab
- Oholot
- Ohrbach
- Oil of Life
- Oistrakh, David Fedorovich
- Okeghem, Jan van
- Okhlah Ve-Okhlah
- Oklahoma City, Archdiocese of
- Oklahoma, Catholic Church in
- Oko, Adolph S.
- Olaf I Tryggvessøn, King of Norway
- Olaf II, King of Norway, St.
- Olah, George A.