This paper reviews research on how nutrient deficiencies affect the developing brain during the prenatal period and early infancy. Nutrient deficiencies – e.g. inadequate protein or iron – have particularly strong effects during the final trimester of pregnancy and first few weeks of life. While the developing brain is resilient and often able to adapt and repair, still its vulnerability to nutrient deficiency means that lack of key nutrients during critical windows of development often results in evidence of brain dysfunction even after the deficiency is corrected. Nutrient deficiencies can affect overall mental function, motor function, and memory.