The Argo profiling float project will enable, for the first time, continuous global observations of the temperature, salinity, and velocity of the upper ocean in near-real time. This new capability will improve our understanding of the ocean's role in climate, as well as spawn an enormous range of valuable ocean applications. Because over 90% of the observed increase in heat content of the air/land/sea climate system over the past 50 years occurred in the ocean <Levitus et al., 2001>, Argo will effectively monitor the pulse of the global heat balance. The end of 2003 was marked by two significant events for Argo. In mid-November 2003, over 200 scientists from 22 countries met at Argo's first science workshop to discuss early results from the floats. Two weeks later, Argo had 1000 profiling floats-one-third of the target total-delivering data. As of 7 May, that total was 1171. The Argo Project Argo is an international effort collecting high-quality temperature and salinity profiles from the upper 2000 m of the ice-free global ocean and currents from intermediate depths. The data come from battery-powered autonomous floats (Figure 1) that drift mostly at depth, where they are stabilized at a constant pressure level by being less compressible than sea water. At typically 10-day intervals, the floats pump fluid into an external bladder and rise to the surface over about 6 hours while measuring temperature and salinity. On surfacing, satellites position the floats, and receive the transmitted data. The bladder then deflates and the float returns to its original density and sinks to drift until the cycle is repeated. Floats are designed to make about 150 such cycles.