Zinc is the second most abundant essential trace element in organisms after iron. Zinc plays a unique role as a component of numerous proteins, a catalytic cofactor for many enzymes, and a component of cellular signaling pathways in various biological reactions. Consequently, zinc deficiency results in multiple symptoms, such as growth retardation, dermatitis, alopecia, and taste disorders. Recent advances in understanding the molecules involved in zinc metabolism have revealed new physiological functions for zinc. This chapter reviews these physiological functions, through a discussion of the history of zinc physiology, zinc content in food, symptoms of zinc deficiency, and zinc absorption in the small intestine. These fundamental views on the significance of zinc will enhance understanding of its importance as a dietary factor.