This review paper describes our current perspective of autism spectrum disorders (ASD), taking into account past, current and future classification systems and the evolving definitions of ASD. International prevalence rates from 1965 to 2012 are presented and key issues, including whether there is an epidemic of autism and what this means in terms of thinking about possible causes of autism, are discussed. Also discussed is the need for high quality national data collection in Australia and the evidence, and lack of evidence, for the many theoretical causes of ASD. The lack of robust classification of autism along with limited high quality evidence base about its prevalence and possible causes leaves ample space for future discoveries