A colourful visual journey from the shoreline to the ocean's depths to celebrate the sheer diversity of life beneath the waves. Three quarters of the ocean has never been seen by humans. Drawing on the recent success of Trees, this companion book explores our oceans, taking readers on a deep dive through the different depth zones - from the shoreline and surface, via the sunlight zone, the twilight and midnight zones and into the great abyss - to chart the richness and diversity of life found in our seas. Each chapter, centred on a different depth zone, begins with a comprehensive introduction, before exploring 15-25 visual themes, from the smallest living things to the largest and the familiar to the little-known. A final chapter on the oceans and us reveals the visual history of human interaction with the deep blue, from discovery and mapping to current issues of the environment and preservation. Stunning photographic content - from microscopic images of tiny individual critters to corals of every hue and the abstract patterns of fish scales - is shown along with a wide range of stunning archival illustrations and specially commissioned infographics that convey complex data in a simple and elegant way. With frequent news stories about the threat to marine life posed by climate change and human behaviours, the oceans are an important subject, and the preservation of biodiversity is crucial for the future of our planet. This book draws attention to the importance of life in our oceans to provide a positive message about the need to preserve it.