The purpose of this protocol is to allow for the careful evaluation of healthy volunteers and individuals with psychiatric disorders or neurodevelopmental disorders, such as autism spectrum disorders. The evaluations will help determine if the participant meets criteria for participation in research protocols of the Pediatric and Developmental Neuroscience Branch (PDN) at the National Institute of Mental Health (NIMH) and other collaborative investigations. This protocol will be the entry point for PDN investigations. Since the entry criteria for these protocols vary, the screening evaluations will also vary. Behavioral evaluations will also be done through this protocol for individuals participating in IRB-approved protocols being conducted by collaborating scientists in NIH. The evaluations might include: a psychiatric interview; a diagnostic interview; developmental and/or cognitive testing; ratings of other psychiatric symptoms; neuropsychological testing; a medical history; a physical exam; blood; and a request for medical records. Parents of minors will be interviewed. Upon conclusion of the screening process, subjects seeking eligibility for PDN protocols will either be offered participation in a research protocol and will sign the appropriate informed consent, or will be considered not appropriate for participation in research and will be discharged from the protocol.