- Of Wind and Winter
- Off the Page
- Offspring
- Ofiara Broni (Księga 8 Kręgu Czarnoksiężnika)
- Ofiucus Asciende
- Og havet var vores himmel
- Ogre Enchanted
- Ogres at Alcatraz Isle
- Oh My Goth
- Ojos de Jade I
- Ojos de Jade II
- Ojos de Jade III
- Ojos en las sombras
- Okami - Aus Feuer geboren
- Okawii
- Okeaniden
- Oksa Pollock
- Oksa Pollock - L'espoir des lendemains
- Okyora & Eggyo
- OKÉÍKPÓ
- Old Friends
- Old Greek Stories
- Old Magic
- Old Neb and the Ghost Ship
- Oldenglen
- Olette
- Oliver and Charley -Supersenders
- Oliver Savoy
- Oliver Smith
- Olivia Engel & Co.
- Olivion's Favorites
- Olli The Old Forest
- OLTRE
- OLTRE - Alice
- Oltre i confini di Hìndamoor
- Oltre le nuvole
- Olympens blod
- Ombra i os
- Ombres
- Omega Awakens
- Omega. I fuochi della guerra
- Omega. L'armata dei ribelli
- Omega: La fine è solo il principio
- Omega: Momenti perduti
- Omens Bite
- Omorfia
- Omvänd (Bok #1 i Vampyrjournalerna)
- On a Wing and a Dare
- On Etruscan Time
- On Fire
- On ne peut plus jamais rentrer chez soi
- On the Day I Died
- On The Run (The Moriya Chronicles: Book 1)
- On the Wolf's Path
- On és el Nadal?
- Once
- Once & Future
- Once Again
- Once Upon
- Once Upon a Dream
- Once Upon A Storm
- Once Upon A Tear
- Once Upon a Time in the North
- Once Upon A Time: Regina Rising
- Once Upon a Unicorn
- Once Upon A War
- Once Upon the Rhine
- Once We Were
- Once We Were Witches
- Once... Tales, Myths and Legends of Faerie
- Onderwereld
- Ondvinter
- One Bad Wish
- One Blood Ruby
- One Dark Throne
- One Earth
- One is Come
- One Jar of Magic
- One Night With the Fae
- One Realm Beyond
- One Thought, Then Gone
- One True King
- One True Queen, Band 1: Von Sternen gekrönt
- One True Queen, Band 2: Aus Schatten geschmiedet (Epische Romantasy von SPIEGEL-Bestsellerautorin Je...
- One Wish
- Only A Phase, Ma: A Gallery of Oddities Story
- Only the Bold (The Way of Steel—Book 4)
- Only the Destined (The Way of Steel—Book 3)
- Only the Valiant (The Way of Steel—Book 2)
- Only the Worthy (The Way of Steel—Book 1)
- Onurun Bedeli (Krallar ve Büyücüler—3. Kitap)
- Onyeka and the Academy of the Sun
- Onyx & Ivory
- Onyx Elixir
- Opal (a Raven Cycle Story)
- Opala
- Opasno ljeto u Mumindolu
- Open Thy Heart
- Operation Sasquatch
- Operation Stargazer
- Operation: Save Santa
- Operculum
- Ophelia and The Marvellous Boy
- Ophelia Scale - Der Himmel wird beben
- Ophelia Scale - Die Sterne werden fallen
- Ophelia Scale - Die Welt wird brennen
- Ophelia Scale - Wie alles begann
- Opie Jones and the Superhero Slug
- Opie Jones Talks to Animals
- Opostos
- Opposite of Always
- Opposition (Lux - Book Five)
- Opstandeling, Pion, Koning (Over Kronen en Glorie—Boek 4)
- Opération Tempête de Sable
- Opętana (Część 12 Wampirzych Dzienników)
- Oracle In The Mist
- Orage sur le Val d'Hespar