- One of Our Conquerors — Volume 4Author: George MeredithLanguage: English
- One of Our Conquerors — Volume 5Author: George MeredithLanguage: English
- One of OursAuthor: Willa CatherLanguage: English
- One Third OffAuthor: Irvin S. (Irvin Shrewsbury) Cobb, Tony SargLanguage: English
- One Woman's LifeAuthor: Robert HerrickLanguage: English
- One Wonderful Night: A Romance of New YorkAuthor: Louis TracyLanguage: English
- Only an IncidentAuthor: Grace Denio LitchfieldLanguage: English
- Only an Irish Boy; Or, Andy Burke's FortunesAuthor: Alger, Horatio, Jr.Language: English
- Onnen orjaAuthor: Eino LeinoLanguage: Finnish
- OntboezemingenAuthor: Carel van NieveltLanguage: Dutch
- Oomphel in the SkyAuthor: H. Beam PiperLanguage: English
- OorlogsvisioenenAuthor: Cyriel BuysseLanguage: Dutch
- Op Eigen WiekenAuthor: Louisa May Alcott, G. W. (Gerardina Wilhelmina) Elberts, Daan de (Daniël) VriesLanguage: Dutch
- Op reis en thuis: Novellen en schetsenAuthor: Justus van MaurikLanguage: Dutch
- Op SamoaAuthor: E. von (Eginhard) BarfusLanguage: Dutch
- Opening a Chestnut BurrAuthor: Edward Payson RoeLanguage: English
- Operation TerrorAuthor: Murray LeinsterLanguage: English
- Operation: Outer SpaceAuthor: Murray LeinsterLanguage: English
- Orley FarmAuthor: Anthony TrollopeLanguage: English
- Orpheu Nº1: Revista Trimestral de LiteraturaAuthor: António Joaquim Tavares Ferro, José de Almada Negreiros, Alvaro de Campos, Ronald de Carvalho, Armando César Cortes-RodriguesLanguage: Portuguese
- Os Bravos do Mindello: Romance HistoricoAuthor: Faustino da FonsecaLanguage: Portuguese
- Os fidalgos da Casa Mourisca: Chronica da aldeiaAuthor: Júlio DinisLanguage: Portuguese
- Os Filhos do Padre AnselmoAuthor: António José da Costa Couto Sá de AlbergariaLanguage: Portuguese
- Os Pobres: Precedido de uma Carta-Prefacio de Guerra JunqueiroAuthor: Raul Brandão, Abílio Manuel Guerra JunqueiroLanguage: Portuguese
- Oscar the Detective; Or, Dudie Dunne, The Exquisite DetectiveAuthor: Old SleuthLanguage: English
- Oscar; Or, The Boy Who Had His Own WayAuthor: Walter AimwellLanguage: English
- Oswald Langdon: or, Pierre and Paul Lanier. A Romance of 1894-1898Author: Hamilton, Levi JacksonLanguage: English
- OthelloAuthor: Wilhelm HauffLanguage: German
- Other People's Business: The Romantic Career of the Practical Miss DaleAuthor: Harriet L. (Harriet Lummis) SmithLanguage: English
- Other People's MoneyAuthor: Emile GaboriauLanguage: English
- Other Things Being EqualAuthor: Emma WolfLanguage: English
- Oulua soutamassaAuthor: Teuvo PakkalaLanguage: Finnish
- Our Elizabeth: A Humour NovelAuthor: Florence A. (Florence Antoinette) Kilpatrick, Ernest ForbesLanguage: English
- Our Friend the CharlatanAuthor: George GissingLanguage: English
- Our Little Korean CousinAuthor: H. Lee M. (Henry Lee Mitchell) PikeLanguage: English
- Our Mr. Wrenn: The Romantic Adventures of a Gentle ManAuthor: Sinclair LewisLanguage: English
- Our Mutual FriendAuthor: Charles DickensLanguage: English
- Our New Neighbors At PonkapogAuthor: Thomas Bailey AldrichLanguage: English
- Our Nig; Or, Sketches from the Life of a Free Black, in a Two-story White House, North: Showing That Slavery's Shadows Fall Even ThereAuthor: Harriet E. WilsonLanguage: English
- Our Pirate Hoard: 1891Author: Thomas A. (Thomas Allibone) JanvierLanguage: English
- Our VillageAuthor: Mary Russell MitfordLanguage: English
- Our World; Or, the Slaveholder's DaughterAuthor: F. Colburn (Francis Colburn) AdamsLanguage: English
- Out Around RigelAuthor: Robert H. WilsonLanguage: English
- Out in the Forty-Five: Duncan Keith's VowAuthor: Emily Sarah HoltLanguage: English
- Out of the AshesAuthor: Ethel Watts Mumford GrantLanguage: English
- Out of the Fog: A Story of the SeaAuthor: Charles K. (Charles Kellogg) OberLanguage: English
- Out of the PrimitiveAuthor: Robert Ames BennetLanguage: English
- Out of the Triangle: A Story of the Far EastAuthor: Mary E. (Mary Ellen) BamfordLanguage: English
- Out with Gun and Camera; or, The Boy Hunters in the MountainsAuthor: Edward StratemeyerLanguage: English
- OutpostAuthor: Jane G. (Jane Goodwin) AustinLanguage: English
- Outward Bound Or, Young America Afloat: A Story of Travel and AdventureAuthor: Oliver OpticLanguage: English
- Over Paradise Ridge: A RomanceAuthor: Maria Thompson DaviessLanguage: English
- Over the PassAuthor: Frederick PalmerLanguage: English
- Over the Rocky Mountains: Wandering Will in the Land of the RedskinAuthor: R. M. (Robert Michael) BallantyneLanguage: English
- Overdue: The Story of a Missing ShipAuthor: Harry Collingwood, W. Herbert (William Herbert) HollowayLanguage: English
- Overland Red: A Romance of the Moonstone Cañon TrailAuthor: Henry Herbert Knibbs, Anton Otto FischerLanguage: English
- Overland: A NovelAuthor: John William De ForestLanguage: English
- Owen Clancy's Happy Trail; Or, The Motor Wizard in CaliforniaAuthor: Burt L. StandishLanguage: English
- Owen Hartley; or, Ups and Downs: A Tale of Land and SeaAuthor: William Henry Giles KingstonLanguage: English
- Paavo KontioAuthor: Eino LeinoLanguage: Finnish