Mild-to-moderate zinc deficiency may be relatively common worldwide, but the public health importance of this degree of zinc deficiency is not well defined. The purpose of this review was to provide a conceptual framework for evaluating the public health importance of maternal zinc deficiency as it relates to fetal growth and development, complications of pregnancy, labor and delivery, and maternal and infant health. The mechanisms through which zinc deficiency could influence health outcomes are well described. The results of experimental studies conducted in animal models have motivated concern about the potential health effects of mild-to-moderate maternal zinc deficiency. Observational studies in human populations have produced strong associations between poor maternal zinc status and various indicators of poor pregnancy outcome, but supplementation trials have not produced strong, or even consistent results. Supplementation trials are needed to define the public health importance of maternal zinc deficiency worldwide.