- O Artico
- O Compost
- O Deserto do Sudoeste
- O Grande Recife
- O is for Octopus
- O Pacifico do Noroeste
- Observando el tiempo
- Ocean
- Ocean Counting
- Ocean Currents and El Niño
- Ocean Friends
- Ocean Speaks
- Ocean! Waves for All
- Oceans
- Octopuses One to Ten
- 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
- Older Than Dirt
- On Beyond Bugs! All About Insects
- On the Job: Underwater Investigators: Plotting Rational Numbers
- On Water
- Once Upon an Elephant
- One Day a Dot
- One Million Trees
- One Turtle's Last Straw
- Only One
- Oona
- Orca Killer Whale
- Orca Rescue!
- 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 Earth
- Our Earth, Our Home
- Our Feathered Friends
- Our House Is on Fire
- Our Moon
- Our Natural Resources
- Our Neighbourhood Houses
- Our Neighbourhood Roads
- Our Planet
- Our Planet: Our Home
- Our Puppet Show
- Our Solar System A Solar System Kids Book
- Our World in Pictures: Trees, Leaves, Flowers & Seeds
- 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 Woods
- Out of This World: Poems and Facts about Space
- Outside the Box: New Ideas!