'The Ocean is Losing its Breath' presents a summary of scientific experiments, observations and numerical models addressing the following questions: How has the oxygen content in the open ocean and coastal waters changed over the past century and through geological time? What are the mechanisms behind this oxygen decline? How is ocean oxygen content predicted to change over the rest of the twenty-first century? What are the consequences of low and declining oxygen concentrations in the marine environment? This document was prepared by a group of concerned scientists from across the world, the IOC expert group, the Global Ocean Oxygen Network GO2 NE, established in 2016, which is committed to providing a global and multidisciplinary view on deoxygenation, with a focus on understanding its various aspects and impacts.