A major roadblock to preventing and more adequately treating autism is that there are many causes and many types. It is currently impossible to determine what type of autism a child has at diagnosis. In order to solve this problem, this study will examine the biology of a large number of children with autism to identify biological signatures of different types of autism. As an extension of the Autism Phenome Project at the M.I.N.D. Institute, preschoolers with ASD and with typical development (TD) will receive full medical evaluation, medical record review, environmental exposure assessment, blood based genetic and immune profiling, structural magnetic resonance imaging (MRI), EEG based studies of auditory processing, and comprehensive developmental and neuropsychological evaluations. This research will lead to identification of several subtypes of autism, which will enable more effective efforts at preventing future cases of autism and treating children with an existing autism diagnosis.