The field of brain imaging for infants is evolving fast. Considerable progress has been made in addressing the great practical challenges that relate to acquiring sufficient data from naturally sleeping infants, for whom sedation is not clinically indicated, and overcoming the technical challenges of analysis. The current challenges facing this evolving field include the consideration of how environmental and clinical factors may alter brain development in the early months of life and defining developmental trajectories. Particularly pressing issues include how prenatal substance exposures affect the very young developing brain. Sex appears to inform not only differences in normal white matter maturation and development, but also differential vulnerability to environmental insults.1 Early neural and behavioral biomarkers may inform early interventions, and these, in turn, may reduce the adverse effects of substances on exposed children. In addition, sex distinction has become increasingly recognized as an important factor to consider in these studies.