Many new aspects of vitamin D have made their appearance. New roles for vitamin D in reproduction, parathyroid function, skin proliferation, and differentiation, in myeloid cell differentiation, and as anti-cancer agents will be new areas of investigation. At the basic science level, much effort will be expended to understand how the vitamin D hormone and its receptor bring about gene expression and how these expressed genes bring about cellular functions of the vitamin D system. Similarly, future work will center on the molecular mechanism of regulation of the hydroxylases of the vitamin D endocrine system. All of this is based on the original discovery that vitamin D must be first metabolically altered before function, producing the vitamin D hormone lα, 25-(OH) ₂D₃, in the proximal convoluted tubule cells of the kidney. There is no doubt that the vitamin D area will continue to expand in the next decade as new functions of the vitamin D system are uncovered.