The immense and opaque Planet Ocean supports one of the largest and poorest known species pools on Earth. The decade long Census of Marine Life program banded together a global network of over 2600 scientists from 80+ nations around the world, who engaged in over 500 research cruises across jurisdictional and disciplinary boundaries to learn what lives in the ocean, what lived in the ocean, and what will live in the future ocean. Census scientists discovered over 1500 new species and counting, scattered from the intertidal to the deep ocean and spanning microbes to fishes, but more importantly advanced our understanding of distribution, diversity and abundance of global ocean life. This novel collaboration utilized technologies from DNA barcoding that provides definitive identifications of even cryptic species, to sonar techniques that rapidly image schools of fish the size of Manhattan, to electronic tags on animals that log oceanographic data from remote regions, tell us where animals move, and show us how they see the ocean. The amalgamation of over 28 million+ data records from thousands of year ago to recent efforts encompasses all ocean habitats and shows blind spots in our taxonomic and biogeographic knowledge. We now know much more about what lives in the oceans, where they live, and why they live there. Importantly, we are better positioned to place this knowledge in the context of what has been lost, what we stand to lose, and in identifying priorities for marine biodiversity research by linking ongoing national programs and emerging opportunities in a proposed initiative on Life in a Changing Ocean.