An attempt is made to outline a satisfactory general theory for the formation of Pacific deep-sea manganese nodules based on a consideration of the time of initiation of formation of the nodules, a mechanism of maintenance of the nodules at the sediment surface and the role of biological productivity of the surface waters in influencing nodule characteristics. Using this model, the principal physical, chemical and distributional features of the nodules and reasons for their differences on a regional scale in the Pacific can be interpreted.