The Southern Ocean is unique among the world's oceans in its linkage across the other major ocean basins, its rich and unusual marine ecosystem, and its interaction between the physical climate system and the biogeochemistry of the region. This paper provides an overview and conclusions of a meeting at the Royal Society in London in which an Earth System Science approach was taken to our present and future understanding of the Southern Ocean. A brief summary of what Southern Ocean science has achieved to date, challenges that need to be confronted, and the key questions for the future within an Earth System Science approach are provided.