Ocean currents are continuous, directed movements of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, the Coriolis force, temperature and salinity differences and tides caused by the gravitational pull of the Moon and Sun. Depth contours, shoreline configurations, and interaction with other currents influence a current's direction and strength.

Ocean currents can flow for great distances, and together they create the great flow of the global conveyor belt which plays a dominant part in determining the climate of many of Earth’s regions. Perhaps the most striking example is the Gulf Stream, which makes northwest Europe much more temperate than any other region at the same latitude. Another example is the Hawaiian Islands, where the climate is cooler (sub-tropical) than the tropical latitudes in which they are located, due to the effect of the California Current on island weather.

In addition to predicting weather and climate, understanding ocean circulation is important for learning how it redistributes heat around Earth, cycles essential nutrients for marine life, and affects the structure and health of ocean ecosystems.

NASA measures many aspects of ocean circulation using powerful technology, such as ocean gliders, buoys, and satellites including the Surface Water and Ocean Topography (SWOT) platform. Anyone interested in measuring and studying ocean circulation can find a variety of data ranging from ocean wind doppler measurements to ocean carbon calculations in NASA's archives.