In this article we present a review of the current literature relating iron and iron deficiency to psychological and neurobiological outcomes in both humans and experimental animals. In particular, we focus on the role of iron during gestation and infancy and the possible impact on neurobehavioral development in the short and long term. In the context of reviewing this literature, the following questions are addressed: (1) What are the neural mechanisms that are directly influenced by iron and iron deficiency? (2) Does iron play a true causal role in determining these outcomes? (3) Is there a sensitive period during which iron deficiency is most harmful?