The most dynamic postnatal brain development takes place during human infancy. Decades of histological studies have identified strong spatial and functional maturation gradients in human brain gray and white matter. The improvements in noninvasive imaging techniques, especially magnetic resonance imaging, magnetic resonance spectroscopy, electroencephalography, magnetoencephalography, positron emission tomography, and near-infrared spectroscopy, have provided unprecedented opportunities to quantify and map the early developmental changes at whole brain and regional levels. Unique to infant brain imaging, tailored infant image acquisition and analysis methods—such as motion correction, high-resolution imaging, optimization of imaging parameters for smaller and immature brain, age-specific brain atlas and parcellation scheme, age-specific white matter tractography, functional connectivity analysis given incomplete brain networks, and advanced gray and white matter segmentation for infant brains should be taken into consideration. Delineating functional, physiological, and structural changes of the infant brain through imaging provides insights into the complicated processes of both typical development and the neuropathological mechanisms underlying various brain disorders with early onset in infancy, such as autistic spectrum disorder. Identification of imaging biomarkers of neurodevelopmental disorders during infancy by leveraging techniques such as machine learning may offer a valuable time window for early intervention.