The Arabian Sea makes contributions to global biogeochemical cycles that are far in excess of what might be expected from its modest size. It experiences extremes in atmospheric forcing, asymmetrically distributed over the region, that brings about exceptionally large hydrographical changes and produce a wide variety of ecosystems or biogeochemical provinces. The diversity and spatio-temporal proximity of these provinces make the region a natural laboratory to investigate present biogeochemical processes, and to apply this knowledge for reconstructing past changes, as well as for predicting future responses of oceanic ecosystems to human-induced climatic change. It has therefore attracted a great deal of attention of oceanographers world over, and has subjected recently to numerous investigations under the aegis of the joint global ocean flux study (JGOFS). The JGOFS results supplemented by those of two other contemporary programmes - the global ocean ecosystem dynamics (GLOBEC) and the world ocean circulation experiment (WOCE) - have immensely improved our understanding of biogeochemistry of this region. Relying largely on these results, this chapter focuses on selected topics of general interest