Autism spectrum disorders (ASD) constitute a major public health problem, affecting one in every 150 children and their families. Unfortunately, there is little understanding of the causes of ASD, and, despite their broad societal impact, many people believe that the overall research program for autism is incomplete, particularly as it relates to the role of environmental factors. The Institute of Medicine’s Forum on Neuroscience and Nervous System Disorders, in response to a request from the U.S. Secretary of Health and Human Services, hosted a workshop called Autism and the Environment: Challenges and Opportunities for Research. The focus was on improving the understanding of the ways in which environmental factors such as chemicals, infectious agents, or physiological or psychological stress can affect the development of the brain. Autism and the Environment documents the concerted effort which brought together the key public and private stakeholders to discuss potential ways to improve the understanding of the ways that environmental factors may affect ASD. The presentations and discussions from the workshop that are described in this book identify a number of promising directions for research on the possible role of different environmental agents in the etiology of autism.