Offering a summary of the current state of knowledge in autism research, Defining Autism looks at the different genetic, neurological and environmental causes of, and contributory factors to autism. It takes a wide-ranging view of developmental and genetic factors, and considers autism's relationship with other conditions such as epilepsy.

Shedding light on the vast number of autism-related syndromes which are all too often denied adequate attention, it shows how, whilst autism refers to a single syndrome, it can be understood as many different conditions, with the common factors being biological, rather than behavioral.