Abstract The ferromanganese nodule resources of the Indian Ocean Nodule Field (IONF) are second only in the world in terms of metal content and abundance. Since it was made known by Mero (1965) that several trillion tonnes of manganese nodules lay in the world oceans, extensive exploration for nodules has been undertaken during the last four decades. The possibility of harvesting an inexhaustible supply of nodules from oceans has resulted in formulation of several national and international programs. India started her search for ferromanganese nodules in 1982. The investigations have resulted in a comprehensive assessment of manganese nodule resources at the ocean-level, and on inter-basin model for nodule growth, albeit with several inaccuracies. We list some of the essential requirements for the formation of nodules including the availability of nucleating materials, presence of metals in water column and sediment, favourable tectonic and physiographic features, helpful acoustically transparent sediment–water interface, low rate of sedimentation, presence of nutrient-rich bottom water mass and an oxidizing environment. We present here an integrated assessment of process of formation of ferromanganese nodules from the IONF, which are variable even on scale of metres. This assessment will help evaluate the metal potential of these nodules more realistically, and the model should bring about a predictive estimate of other nodule-bearing areas in the world oceans.