Autism spectrum disorders (ASDs) are a group of developmental disabilities characterised by impairments in social interaction and communication and by restricted, repetitive, and stereotyped patterns of behaviour. Symptoms typically are apparent before age 3 years. The complex nature of these disorders, coupled with a lack of biologic markers for diagnosis and changes in clinical definitions over time, creates challenges in monitoring the prevalence of ASDs. Accurate reporting of data is essential to understand the prevalence of ASDs in the population and can help direct research. This book provides a parent's guide to autism spectrum disorder with a focus on prevalence; suggested environmental factors; and federal financing research.