Micronutrient deficiencies affect billions of people worldwide and often coexist in developing countries due to consumption of diets lacking nutrient diversity. Thus, it is important to consider how micronutrients such as copper (Cu), iron (Fe), and iodine interact physiologically. Cu, Fe, and iodine/thyroid hormone (TH) deficiencies lead to similar brain development deficits, suggesting these micronutrient deficiencies share a common mechanism contributing to the observed derangements. Previous studies in rodents and humans indicate that Cu and Fe deficiencies during adolescence or adulthood lead to impaired TH status. However, prior to this thesis research, relationships between Fe or Cu deficiencies and thyroidal status had not been assessed in the most vulnerable population, the developing fetus/neonate. My first two studies showed that Fe deficiency lowers newborn rat circulating and brain TH concentrations and alters TH-regulated brain gene expression. In a third study, Fe deficiency exacerbated the effect of mild TH insufficiency on neonatal thyroidal status and brain TH-responsive gene expression. Together, these novel findings suggest that impaired neonatal thyroidal status may contribute to some of the brain developmental abnormalities associated with fetal/neonatal Fe deficiency. Fe deficiency also has significant impacts on the developing brain independent of effects on thyroid function. In humans, Fe deficiency often results in anemia, reduced blood oxygen carrying capacity. Decreased oxygen delivery to the brain can induce a compensatory increase in blood vessel outgrowth. My final study demonstrated, for the first time, that Fe deficiency anemia increases blood vessel growth in the neonatal rat brain. The functional contribution of increased vasculature to the developing Fe-deficient brain is unknown but could be adaptive, maladaptive, or both. In summary, my thesis research exploring micronutrient interactions during brain development has identified two novel potential contributors to the brain developmental derangements associated with Fe deficiency: impaired neonatal thyroid function and increased neonatal brain vasculature.