Autism Spectrum Disorder (ASD) is the most common developmental disability in the United States and occurrences of the disorder continue to rise. ASD is defined as exhibiting social and communication deficits and repetitive or stereotypic behaviors. ASD has changed greatly over the years in terms of what is known about its cause, its increase in prevalence, and the treatment methods available. A notable recent change to ASD is a significant transformation in the diagnostic criteria that incorporated previously distinct disorders into a spectrum. The impact of the diagnostic changes on cost and treatment are yet to be determined, but will need to be considered as advances for treatment and care for individuals with the disorder over their lifetime emerge.