Ocean is an ambitious history of the pre-Columbian Atlantic Ocean, a story that begins with the formation of the mid-Atlantic ridge some 200 million years ago and ends with the Castilian conquest of the Canary Islands in the fifteenth century, which provided a template for the methods used by the Spanish in their colonisation of the New World.

John Haywood argues that the perception that Atlantic history begins with the first voyage of the celebrated Genoese navigator is a mistaken one, and that the seafaring and shipbuilding skills that enabled European global exploration and expansion did not arrive fully formed in the fifteenth century, but were learned over centuries and millennia in the Atlantic and its marginal seas. The pre-Columbian history of the Atlantic is the story of how Europeans learned to master the oceans. It is, therefore, key to understanding why it was Europeans, and not any of the world's other seafaring peoples, who 'discovered' the world.

Ocean is informed by the author's extensive travels in and around the Atlantic Ocean, crossing Newfoundland's Grand Banks, the Sea of Darkness and the weed-covered Sargasso Sea to make landfall at locations as diverse as Vinland, Greenland, the Faroes and the Cape Verde Islands. Populated by a heterogeneous and multi-ethnic cast of seafarers, fishermen, monks, merchants and dreamers, this is an in-depth history of a neglected subject, fusing geology, geography, mythology, cosmology, developing maritime technologies and the early history of exploration to narrate an enthralling and intriguing story that lies at the very heart of Europe's modern history and its relationship with the rest of the world. A history on a grand scale, Ocean offers the reader a feast of historical storytelling that will appeal to readers of David Abulafia, Simon Winchester and Michael Pye.