Abstract Numerous technologies are available for studying the brain basis of developmental disabilities, each of which has its advantages and disadvantages. These include electroencephalography (EEG), event-related potentials (ERP), magnetoencephalography (MEG), near-infrared optical tomography (NIROT), positron emission tomography (PET), magnetic resonance imaging (MRI), and magnetic resonance spectroscopy (MRspect). This chapter focuses on two technologies—ERP and MRI—which are increasingly being used in research on developmental disabilities. It discusses how each methodology works and what kinds of research questions each is well suited to answer. It illustrates the application of these methods in four specific genetic disorders: Down syndrome, Prader-Willi syndrome, Williams syndrome, and fragile X syndrome. Finally, the chapter discusses gaps in current research, issues of experimental design, and suggests directions for future studies.