This primer introduces a Special Section on brain imaging, which includes a commentary and 10 data papers presenting applications of brain imaging to questions on developmental psychopathology. This primer serves two purposes. First, the article summarizes the strength and weaknesses of various brain-imaging techniques typically employed in research on developmental psychopathology. Second, the article places research on brain imaging in a broader context by discussing particular limitations and utilities of imaging. Specifically, while brain imaging is currently of limited clinical utility, work in this area is beginning to shape clinical thinking. Brain-imaging research offers a unique opportunity to constrain theories of pathophysiology based on understandings of brain function. This effect promises to open avenues for novel treatments.