- O Artico
- O Compost
- O Deserto do Sudoeste
- O Grande Recife
- O Mundo dos Hopfs
- O Pacifico do Noroeste
- Oak Trees
- Observando el tiempo
- Ocean Animals (Animal Planet Animal Bites)
- Ocean Counting
- Ocean Currents and El Niño
- Ocean Emporium
- Ocean Engineering and Designing for the Deep Sea
- Ocean Friends
- Ocean Speaks
- Knowledge Encyclopedia Ocean!
- Ocean! Waves for All
- Oceans
- Oceans Inside Out
- Octopuses One to Ten
- Odd Dog
- Odin, Dog Hero of the Fires
- Oh No, Astro!
- Oh Say Can You Say What's the Weather Today? All About Weather
- Oh Say Can You Seed? All About Flowering Plants
- Oil
- Oil and Pipelines
- Oil's Quest
- Older Than Dirt
- Olguita Oruguita explica los virus y compañía
- Olympic Sport: The Whole Muscle-Flexing Story
- On a Beam of Light
- On a Beam of Light
- On Beyond Bugs! All About Insects
- On Our Nature Walk
- On Our Nature Walk Read-Along (Enhanced Edition)
- On the Farm
- On the Job: Underwater Investigators: Plotting Rational Numbers
- On Water
- Once Upon an Elephant
- One Day a Dot
- One Home
- One Million Trees
- One Moment in Time
- One Turtle's Last Straw
- One World, Many Colors
- Only One
- Oona
- Operation Ouch!: The HuManual
- Operazione SalvaPianeta! (Ediz. Alta Leggibilità)
- Optical Physics for Babies
- Orange
- Orca Killer Whale
- Orca Rescue!
- Orcas of the Salish Sea
- Orcas of the Salish Sea Read-Along (Enhanced Edition)
- Order of Operations
- Organic Chemistry for Babies
- Origami Galaxy for Kids Ebook
- Oscar der Ballonfahrer entdeckt die Tiere des Teiches!
- Oscar der Ballonfahrer – Hotte von Hüh ist ein Pferd
- Otis and Will Discover the Deep
- Otis the Owl
- Otis, el búho
- Our Amazing Sun
- Our Carbon Footprint
- Our Earth
- Our Earth, Our Home
- Our Feathered Friends
- Our House Is on Fire
- Our Island
- Our Moon
- Our Natural Resources
- Our Neighbourhood Houses
- Our Neighbourhood Roads
- Our Planet
- Our Planet: Our Home
- Our Puppet Show
- Our Solar System
- Our Solar System A Solar System Kids Book
- Our World Is Relative
- Our World Out of Balance: Understanding Climate Change and What We Can Do
- Out of Sight Till Tonight! All About Nocturnal Animals
- Out of the Ashes
- Out of the Woods
- Out of This World: Poems and Facts about Space
- Outdoor Math
- Outdoor Science Lab for Kids
- Outer Space
- Outside the Box: New Ideas!
- Over and Under the Canyon
- Over and Under the Pond
- Overpopulation Eco Facts
- Overview, Young Explorer's Edition