In association with planned networks of drifting instruments and satellite-based sensor systems, the establishment of Oceanographic Observatories at select sites around the world's oceans is recommended. The Ocean Observatories will collect time series of surface meteorology, of the air-sea exchanges of heat, freshwater, and momentum, and of full depth profiles of ocean temperature, salinity, velocity and biogeochemical parameters (as sensor systems develop). New mooring and instrumentation technology makes it possible to maintain such observatories at a fraction of the cost of the previous ocean weather stations. The Ocean Observatories will constitute a critical component of the Global Ocean Observing System (GOOS) through helping to develop a description and an understanding of the ocean's role in climate. Time series from the Observatories will provide the key information needed to construct accurate fields of the air-sea fluxes. They will also document water mass formation and transformation, quantify the transports of the major ocean current systems, resolve variability in the vertical structure of the ocean stratification and circulation, and document the role of eddy processes in the transport of heat and other properties.