- O Pioneers!
- O Solitude! If I Must With Thee Dwell
- O'Conors of Castle Conor
- O'Flaherty V.C. : a recruiting pamphlet
- O+F
- O. Henry Memorial Award Prize Stories of 1919
- O. Henry Memorial Award Prize Stories of 1920
- O. Henry Memorial Award Prize Stories of 1921
- Oak Openings
- The Oakdale Affair
- Obed Hussey Who, of All Inventors, Made Bread Cheap
- Obiter Dicta
- Objects of Interest. Compiled Especially with Reference to Those Numerous Visitors Who Can Spare but Two or Three Days to Make the Tour of the Island.
- The Oblong Box
- Observations By Mr. Dooley
- Observations Upon the Windward Coast of Africa
- Observations and Reflections Made in the Course of a Journey through France, Italy, and Germany, Vol. I
- Observations of a Retired Veteran
- Observations of an Orderly Some Glimpses of Life and Work in an English War Hospital
- Observations on the Effects of the Corn Laws, and of a Rise or Fall in the Price of Corn on the Agriculture and General Wealth of the Country
- Observations upon the Prophecies of Daniel, and the Apocalypse of St. John
- The Obstacle Race
- Occasional Poems Part 3 from Volume IV., the Works of Whittier: Personal Poems
- Occasional Thoughts in Reference to a Vertuous or Cristian life
- Occult Chemistry Clairvoyant Observations on the Chemical Elements
- An Occurrence at Owl Creek Bridge
- October 1910
- October Vagabonds
- The Octopus : A story of California
- Odd Charges Odd Craft, Part 13.
- Odd Craft, Complete
- Odd Man Out Sailor's Knots, Part 6.
- The Odd Women
- The Odds And Other Stories
- Ode
- Ode On Indolence
- Ode On Melancholy
- Ode To Psyche
- Of Captain Mission
- Of Essay Writing
- 'Of Genius', in The Occasional Paper, and Preface to The Creation
- Of Human Bondage
- Of Superstition And Enthusiasm
- Of The Delicacy Of Taste And Passion
- Of The Liberty Of The Press
- Of The Rise And Progress Of The Arts And Sciences
- Of The Standard Of Taste
- Of Tragedy
- Of the Orthographie and Congruitie of the Britan Tongue A Treates, noe shorter than necessarie, for the Schooles
- Of the Reaction of Mechanical and Scientific Progress upon Human life and Thought
- Off on a Comet! a Journey through Planetary Space
- Off-Hand Sketches
- Official Report of the Exploration of the Queen Charlotte Islands for the Government of British Columbia
- Oh, Money! Money!
- Okewood of the Secret Service
- Oklahoma and Other Poems
- An Old Babylonian Version of the Gilgamesh Epic
- The Old Bachelor: a Comedy
- Old Ballads
- The Old Bell of Independence; Or, Philadelphia in 1776
- The Old Bush Songs
- Old Calabria
- Old Caravan Days
- Old Christmas
- Old Creole Days
- The Old Curiosity Shop
- The Old English Baron: a Gothic Story
- Old English Libraries
- Old English Sports
- An Old Fashioned Story
- Old Fires and Profitable Ghosts
- Old French Romances
- Old Friends, Epistolary Parody
- Old Fritz and the New Era
- Old Gorgon Graham More Letters from a Self-Made Merchant to His Son
- Old Granny Fox
- The Old Gray Homestead
- Old Greek Folk Stories Told Anew
- Old Greek Stories
- The Old Homestead
- Old Indian Days
- Old Indian Legends
- Old John Brown, the man whose soul is marching on
- Old Kaskaskia
- Old Lady Mary A Story of the Seen and the Unseen
- Old Lady Number 31
- Old Love Stories Retold
- An Old Maid
- The Old Man in the Corner
- The Old Man of the Sea Ship's Company, Part 11.
- The Old Masters and Their Pictures For the Use of Schools and Learners in Art
- The Old Merchant Marine; A chronicle of American ships and sailors
- Old Mission Stories of California
- Old Mortality, Complete
- Old Mortality, Volume 1.
- Old Mortality, Volume 2.
- Old Mother West Wind
- The Old Northwest : A chronicle of the Ohio Valley and beyond
- The Old Peabody Pew
- Old Portraits, Modern Sketches, Personal Sketches and Tributes Complete, Volume VI., the Works of Whittier
- Old Portraits, Part 1, from Volume VI., The Works of Whittier: Old Portraits and Modern Sketches
- Old Rose and Silver
- Old Saint Paul's A Tale of the Plague and the Fire
- Old Spookses' Pass, Malcolm's Katie, and other poems
- Old St. Paul's Cathedral
- The Old Stone House
- An Old Town By the Sea
- The Old Wives' Tale
- Old and New Masters
- Old-Fashioned Fairy Tales
- An Old-Fashioned Girl
- Old-time Stories, Fairy Tales and Myths Retold by Children
- The Olden Time Series, Vol. 1: Curiosities of the Old Lottery Gleanings Chiefly from Old Newspapers of Boston and Salem, Massachusetts
- The Olden Time Series, Vol. 5: Some Strange and Curious Punishments Gleanings Chiefly from Old Newspapers of Boston and Salem, Massachusetts
- Oldport Days
- Ole Mammy's Torment
- Oliver Cromwell
- Oliver Goldsmith A Biography
- Oliver Twist
- Oliver Wendell Holmes (from Literary Friends and Acquaintance)
- Olivia in India
- Omoo
- On A Dream
- On Being Human
- On Books and the Housing of Them
- On Commando
- On Compromise
- On Dreams
- On First Looking Into Chapmans Homer
- On Generation And Corruption
- On Heroes and Hero Worship and the Heroic in History
- On Horseback
- On Interpretation
- On Land and Sea at the Dardanelles
- On Liberty
- On Longevity And Shortness Of Life
- On Memory And Reminiscence
- On Nothing and Kindred Subjects
- On Our Selection
- On Picket Duty, and Other Tales
- On Prophesying By Dreams
- On Sense And The Sensible
- On Shakespear. 1630
- On Sitting Down To Read King Lear Once Again
- On Sleep And Sleeplessness
- On Some Fossil Remains of Man
- On Something
- On Sophistical Refutations
- On The Art of Reading
- On The Blockade
- On The Death Of A Fair Infant Dying Of A Cough
- On The Gait Of Animals
- On The Generation Of Animals
- On The Heavens
- On The Improvement Of The Understanding
- On The Lord Gen. Fairfax At The Seige Of Colchester
- On The Morning Of Christs Nativity
- On The Motion Of Animals
- On The Nature Of Things
- On The New Forcers Of Conscience Under The Long Parliament
- On The Parts Of Animals
- On The Soul
- On The University Carrier
- On Time
- On Visiting The Tomb Of Burns
- On With Torchy
- On Youth And Old Age, On Life And Death, On Breathing
- On the Advisableness of Improving Natural Knowledge
- On the Banks of the Ohio
- On the Choice of Books
- On the Church Steps
- On the Decay of the Art of Lying
- On the Economy of Machinery and Manufactures
- On the Edge of the War Zone From the Battle of the Marne to the Entrance of the Stars and Stripes
- On the Evolution of Language First Annual Report of the Bureau of Ethnology to the Secretary of the Smithsonian Institution, 1879-80, Government Printing Office, Washington, 1881, pages 1-16
- On the Firing Line
- On the Fringe of the Great Fight
- On the Frontier
- On the Indian Sect of the Jainas
- On the King's Service Inward Glimpses of Men at Arms
- On the Makaloa Mat
- On the Method of Zadig
- On the Nature of Things
- On the Origin of Species By Means of Natural Selection, or, the Preservation of Favoured Races in the Struggle for Life
- On the Origin of Species: or, the Causes of the Phenomena of Organic Nature
- On the Pampas
- On the Relations of Man to the Lower Animals
- On the Ruin of Britain
- On the Seashore
- On the Spanish Main Or, Some English forays on the Isthmus of Darien.
- On the Study of Words
- On the Study of Zoology
- On the Track
- On the Trail An Outdoor Book for Girls
- On the Trail of Grant and Lee
- Once Aboard the Lugger
- Once Upon A Time
- Once Upon a Time in Connecticut
- One Basket
- One Day More A Play In One Act
- One Day's Courtship
- The One Great Reality
- One Hundred Best Books
- One Hundred and Twenty Asiatic Love Poems
- One Man in His Time
- One Third Off
- One Thousand Questions in California Agriculture Answered
- The One Woman
- One Woman's Life
- One Wonderful Night A Romance of New York
- One Young Man The simple and true story of a clerk who enlisted in 1914, who fought on the western front for nearly two years, was severely wounded at the battle of the Somme, and is now on his way back to his desk.
- One of Ours
- The Onlooker, Volume 1, Part 2
- The Only True Mother Goose Melodies
- Only an Incident
- Only an Irish Boy Andy Burke's Fortunes
- Oonomoo the Huron
- The Open Air
- The Open Door, and the Portrait. Stories of the Seen and the Unseen.
- An Open Letter on Translating
- The Open Secret of Ireland
- An Open-Eyed Conspiracy; an Idyl of Saratoga
- Openings in the Old Trail
- Operation R.S.V.P.
- Operation Terror
- Operation: Outer Space
- The Opinions of a Philosopher
- The Opium Habit
- Options
- Or Three Seventh Years Two Centuries Ago
- Or When the World Was Younger
- Or Winning the Ferberton Prize
- Or the Hermit of Fern Island
- Or the Longest Journey on Record
- Or the Strange Cruise of the Tartar
- Or, A Discovrse Tending To Prove That 'Tis Probable There May Be Another Habitable World In That Planet
- Or, A Hunt for Fun and Fortune
- Or, A Treatise of Hermaphrodites
- Or, At Railwood Building in Earnest
- Or, Daring Adventures in South America
- Or, Fighting the Mine Swindlers
- Or, Helping the Dormitory Fund
- Or, Humors on the Border; A story of the Old Virginia Frontier
- Or, Jasper Parloe's Secret
- Or, Memories of the Past
- Or, Merry Days Indoors and Out
- Or, Pastoral and Local Poetry
- Or, Seeking Fortune on the Turn of a Pick
- Or, Stirring Adventures in Africa
- Or, The Beginnings of an Empire
- Or, The Buddha and the Christ, Part I
- Or, The Courier of the Czar
- Or, The Crime of the Midnight Express
- Or, The Dread Mystery of the Million Dollar Breakwater
- Or, The Evidence of Holy Scripture and the Church, Against the Invocation of Saints and Angels, and the Blessed Virgin Mary
- Or, The Great Adams Express Robbery
- Or, The Great Quadrangle Mystery
- Or, The Naval Officer
- Or, The Old Hunter's Treasure Box
- Or, The Right Road and the Wrong
- Or, The Search for a Lost Mine
- Or, The Strange Cruise of the Steam Yacht
- Or, The Young Express Agent
- Or, Wild England
- Or, Wintering in the Sunny South
- Or, a chase for a fortune
- Or, camping and tramping for fun and health
- Or, doing their best for the soldiers
- Or, doing their bit for the soldier boys
- Or, from Boarding School to Ranch and Range
- Or, in Quest of the Field of Diamonds
- Or, pictures of life and scenery in the woods of Canada
- Or, the African Quadroon : a Story of the Slave Coast
- Or, the Captives of the Great Earthquake
- Or, the End of the Silver Trail
- Or, the Fighting Canadians of Vimy Ridge
- Or, the Mystery of the Centre of the Earth
- Or, the Mystery of the Old Custer Trail
- Or, the Pretended Riot Explained
- Or, the Secret of Ruby Mountain
- Or, the Secret of the Lost Claim
- Or, the Steam Man of the Prairies
- Or, the Strange Cruise of the Submarine Wonder
- Or, the Wild Riders of the Plains. The Veritable Adventures of Hal Hyde and Ned Brown, on Their Journey Across the Great Plains of the South-West
- Or, the Young Derelict Hunters
- Or, the hermit of Moonlight falls
- Or, the secret of the island cave
- Or, the stirring cruise of the motor boat Gem
- The Orange Fairy Book
- The Orange-Yellow Diamond
- Orations
- The Ordeal A Mountain Romance of Tennessee
- The Oregon Trail: sketches of prairie and Rocky-Mountain life
- Organic Gardener's Composting
- The Organization of the Congregation in the Early Lutheran Churches in America
- Oriental Encounters Palestine and Syria, 1894-6
- Oriental Literature The Literature of Arabia
- Origin of Species
- The Origin of Species by means of Natural Selection, 6th Edition
- An Original Belle
- Original Letters and Biographic Epitomes
- Original Pieces in Prose and Verse
- Oroonoko: Or, The Royal Slave
- Orpheus in Mayfair and Other Stories and Sketches
- Orthodoxy
- Osage Traditions
- Oscar The Boy Who Had His Own Way
- Oscar the Detective Or, Dudie Dunne, The Exquisite Detective
- Othello
- Other People's Money
- Other Poems
- Other Stories
- Other Tales of the California Missions
- Other Things Being Equal
- Other Verses
- Other Worlds Their Nature, Possibilities and Habitability in the Light of the Latest Discoveries
- Others
- Otto of the Silver Hand
- Our American Cousin
- Our Boys Entertaining Stories by Popular Authors
- Our Catholic Heritage in English Literature of Pre-Conquest Days
- Our Churches and Chapels
- Our Day In the Light of Prophecy
- Our Elizabeth A Humour Novel
- Our Foreigners A Chronicle of Americans in the Making
- Our Friend John Burroughs
- Our Friend the Charlatan
- Our Friend the Dog
- Our Gift
- Our Government: Local, State, and National: Idaho Edition
- Our Holidays Their Meaning and Spirit; retold from St. Nicholas
- Our Hundred Days in Europe
- Our Lady Saint Mary
- Our Legal Heritage
- Our Legal Heritage : 600-1776 King Aehelbert - King George III
- Our Legal Heritage, 5th Ed.
- Our Little Korean Cousin
- Our Master Thoughts for Salvationists about Their Lord
- Our Mr. Wrenn
- Our Mr. Wrenn, the Romantic Adventures of a Gentle Man
- Our Mutual Friend
- Our Navy in the War
- Our Pilots in the Air
- Our Saviour
- Our Unitarian Gospel
- Our Village
- Our War with Spain for Cuba's Freedom
- Our World, Or, the Slaveholder's Daughter
- 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 there
- Out To Win The Story of America in France
- Out of Time's Abyss
- Out of the Ashes
- Out of the Fog
- Out of the Primitive
- Out of the Triangle: a story of the Far East
- Out with Gun and Camera
- Outback Marriage, an : a story of Australian life
- An Outcast of the Islands
- The Outdoor Chums After Big Game Or, Perilous Adventures in the Wilderness
- The Outdoor Chums The First Tour of the Rod, Gun and Camera Club
- The Outdoor Girls at Ocean View Or, The Box That Was Found in the Sand
- The Outdoor Girls in a Motor Car The Haunted Mansion of Shadow Valley
- The Outdoor Girls in the Saddle Or, The Girl Miner of Gold Run
- The Outdoor Girls on Pine Island Or, A Cave and What It Contained
- The Outlaw of Torn
- The Outlet
- An Outline of the Relations between England and Scotland (500-1707)
- Outlines of English and American Literature : an Introduction to the Chief Writers of England and America, to the Books They Wrote, and to the Times in Which They Lived
- Outlines of Lessons in Botany, Part I; from Seed to Leaf
- Outlines of an English Romance
- Outlines of the Earth's History A Popular Study in Physiography
- Outpost
- The Oval Portrait
- Over 300 Useful and Valuable Helps About the Home, Carefully Compiled and Arranged in Convenient Form for Frequent Use
- Over Here
- Over Prairie Trails
- Over Strand and Field
- Over The Hill And Over The Dale
- Over There
- Over the Pass
- Over the Side Captains All, Book 6.
- Over the Sliprails
- Over the Teacups
- Over the Top
- Overland
- Overruled
- Owindia : a true tale of the MacKenzie River Indians, North-West America
- Oxford
- Oxy-Acetylene Welding and Cutting Electric, Forge and Thermit Welding together with related methods and materials used in metal working and the oxygen process for removal of carbon
- Ozma of Oz