The Bay of Bengal has a surprisingly large influence on the world. It nurtures the South Asian summer monsoon, a tremendous ocean-atmosphere-land phenomenon that delivers freshwater to more than a third of the human population on this planet. During summer, southwesterly winds gather moisture from the ocean and carry it deep inland over the Indian subcontinent, bringing welcome rains to a parched land. During winter, the winds reverse to northeasterly, and the ocean circulation responds by dispersing the terrestrial freshwater runoff concentrated in the northern part of the bay. This freshwater impacts the ocean’s structure, circulation, and biogeochemistry in numerous ways and, through modification of sea surface temperature, feeds back to influence air-sea fluxes. Because the atmosphere obtains its moisture and heat for convection from the ocean, the interplay between ocean and atmosphere is crucial for the development and sustenance of the monsoon.