Since the Challenger Expedition in the 1870s, oceanographers have explored and sampled across two-thirds of our planet using ships as primary observational platforms. In the past several decades, satellite-observing systems have provided a much-needed synoptic overview of ocean surface characteristics. A growing number of instrumented moorings have been deployed in selected portions of the global ocean to obtain more continuous information about upper oceanic and atmospheric processes. Insights, knowledge, and models based on this exploratory phase of oceanography have resulted in growing recognition of the diversity and the complexity of processes that operate within and beneath the ocean basins. Indeed, we cannot answer many of the questions we can now pose using only the tools of the present. For this reason, the ocean sciences are on the threshold of a new era in which we must enter the entire ocean environment and establish interactive networks for ill situ, adaptive observations of, and experiments with, key phenomena in the global earth-ocean system.