O'Brien, Edward J. (Edward Joseph Harrington), 1890-1941
- The Forgotten Threshold (English)
O'Brien, Fitz James, 1828-1862
- The Diamond Lens (English)
O'Brien, Frederick, 1869-1932
- Mystic Isles of the South Seas. (English)
- White Shadows in the South Seas (English)
O'Brien, George
- An Essay on Mediaeval Economic Teaching (English)
O'Brien, Jack
- Into the Jaws of Death (English)
O'Brien, Seumas
- Duty, and other Irish Comedies (English)
O'Conner, T. P.
- Sketches in the House (1893) (English)
O'Connor, John Charles
- English-Esperanto Dictionary (English)
O'Cotter, Pat
- Rhymes of a Roughneck (English)
O'Donnell, Elliott, 1872-1965
- Animal Ghosts
Or, Animal Hauntings and the Hereafter (English) - Scottish Ghost Stories (English)
- The Sorcery Club (English)
O'Grady, Standish, 1846-1928
- Early Bardic Literature, Ireland. (English)
- The Coming of Cuculain (English)
O'Higgins, Harvey Jerrold, 1876-1929
O'Keefe, John
- As Long As You Wish (English)
O'Kelly, Seumas, 1881-1918
- Waysiders (English)
O'Mahony, John
O'Meara, James, 1825-1903
- The Vigilance Committee of 1856 (English)
O'Neill, Elizabeth (Elizabeth Speakman), 1877-
- Stories That Words Tell Us (English)
O'Neill, Eugene, 1888-1953
- Anna Christie (English)
- The First Man (English)
- The Hairy Ape (English)
- The Straw (English)
O'Reilly, A. J. (Augustine J.)
- Alvira, the Heroine of Vesuvius (English)
O'Reilly, John Boyle, 1844-1890
- The King's Men
A Tale of To-morrow (English)
O'Rourke, John
- The History of the Great Irish Famine of 1847 (3rd ed.) (1902)
With Notices of Earlier Irish Famines (English)
O'Squarr, Charles-M. Flor
- Les fantômes (French)
Oahu College
- The Oahu College at the Sandwich Islands (English)
