The environmental integrity and sustainable productivity of the ocean, our coasts and coastal watersheds, and the Great Lakes play a central role in the well-being of all Americans. Every day, the marine environment supplies a multitude of products and services that enhance and support the lives and livelihoods of citizens. In 2011, Americans, on average, ate 15 pounds of fish and shellfish per person - 4.7 billion pounds all together - making the United States second in the world in total seafood consumption. Offshore oil production in Federal waters accounts for fully 24 percent of total U.S. crude oil production. More than half of the United States population lives in coastal watershed counties, and these counties generate 58 percent ($8.3 trillion) of the Nation's gross domestic product (GDP)-even though they comprise only 25 percent of the Nation's land area. If American coastal watershed counties were considered an individual country, that country would have a GDP higher than that of China. Recognizing the central role these environments and their resources play, and the many sometimes competing demands placed on them, President Obama issued Executive Order 13547, Stewardship of the Ocean, Our Coasts, and the Great Lakes, on July 19, 2010. The Executive Order established a comprehensive National Ocean Policy to improve the Nation's stewardship of the ocean, our coasts, and the Great Lakes. The Policy, which adopts the Final Recommendations of the Interagency Ocean Policy Task Force, calls for use of the best available science to inform decisions affecting these essential ecosystems as well as to enhance humanity's capacity to understand and respond to a changing global environment. Full implementation of the National Ocean Policy will require significant progress in ocean science and more effective application of research results to aid decision-making. These two important concepts drove the selection of issues that frame this document, Science for an Ocean Nation. Science for an Ocean Nation sets priorities for scientific research that support the National Ocean Policy goal of balancing the productive use of the marine environment with its stewardship and protection. It represents the consensus view of 25 Federal agencies regarding key ocean science research areas and incorporates extensive input from outside the Federal Government. This report is constructed around six societal themes that frame ocean research in terms of the needs of Americans. Within these societal themes, Science for an Ocean Nation presents research priorities with the greatest potential to provide benefits to the Nation. This report builds on its predecessor, Charting the Course for Ocean Science in the United States for the Next Decade ("Charting the Course"), by updating research priorities, addressing emerging areas of research, and highlighting accomplishments resulting from Charting the Course. It also highlights cross-cutting capabilities and approaches that can help provide the technological advancements, broad perspective, and community structure needed to address the research priorities. The themes that frame Science for an Ocean Nation represent key areas of interaction between human society and the ocean. The research priorities within each societal theme draw upon both natural and social sciences and aim to improve the tools required not only to carry out research but also to translate, disseminate, and apply the results of that research to address pressing issues facing the Nation and the world.