Autism spectrum disorder (ASD) is a neurodevelopmental disorder described in the Diagnostic and Statistical Manual of Mental Disorders (5th ed., American Psychiatric Association, Diagnostic and statistical manual of mental disorders, 5th edn. Author, Washington, DC, 2013) as including impairments in social communication and restricted and repetitive behavior patterns. Prevalence estimates vary but according to the Centers for Disease Control and Prevention, (MMWR Surveill Summ 63(2):1–22, 2014), 1 in 68 children have ASD.

Impairments in social communication are a defining feature of ASD although there is a great deal of variability in the severity of these impairments and the way in which they manifest across individuals. In this book, we focus on prelinguistic communicators. The prelinguistic period of communicative development refers to the time between birth and when a child begins to use words meaningfully. Typically, infants experience the prelinguistic period from birth to around 18 months of age, during which time they progressively develop intentional and symbolic forms of communication representing a range of communicative functions.