Pica, the purposive consumption of nonfood substances, is a millennia-old nutritional enigma. Its worldwide ubiquity, prevalence among pregnant women and children, and association with both positive and negative health outcomes, especially micronutrient deficiencies, underscore the importance of understanding this behavior. Multiple proposed etiologies of pica are reviewed, including cultural expectations, psychological stress, hunger, dyspepsia, micronutrient deficiencies (Fe, Zn, and Ca), and protection against toxins and pathogens. Currently available data, although limited, best support the protection hypothesis as a cause of most types of pica, although some evidence suggests that pagophagy (ice consumption) may occur during iron deficiency. It is possible that the binding capacity of pica substances explains the association with micronutrient deficiencies; earth, starch, etc. may render micronutrients in …