The two conventions signed at the United National Conference on Environment and Development (UNCED, Rio de Janeiro, 1992), The Framework Convention on Climate Change and The Convention on Biological Diversity, and the recommendations of Agenda 21, Chapter 17, require the establishment of an adequate observing system to develop understanding and to monitor change. To do this, continuing systematic, long-term, global observations of marine physical, chemical, and biological conditions, analogous to the World Weather Watch, operating under the auspices of the World Meteorological Organization (WMO), are required. Guided by the Intergovernmental Oceanographic Commission (IOC), WMO, the United National Environmental Program (UNEP) and the International Council for Scientific Unions (ICSU), the planning for the Global Ocean Observing System (GOOS) is being initiated. One aspect of the planning for GOOS is directed at considerations of the health of the ocean. The Health of the Ocean (HOTO) Module of GOOS will provide a basis for the assessment of the state and trends in the marine environment as it is affected by anthropogenic activities, including, inter alia, increased risks to human health, harm to marine resources, alterations of natural change and general ocean health. An international panel was formed under the leadership of the IOC to achieve this goal. The purpose of this document is to outline the strategy and detailed scientific and technical design for the Assessment and Prediction of the Health of the Ocean (HOTO) Module of GOOS. The discussion that follows is an overview of deliberations that have taken place over the last three years.