The importance of implementing an early intervention programme in Autistic Spectrum Disorders (ASD) is widely acknowledged. Applied Behaviour Analysis (ABA) is one particular intervention model that has received increasing attention. The essence of ABA is a careful analysis of behavior, adapted from the initial studies of Skinner, which aims to develop skills and reduce maladaptive behaviours in individuals with ASD. A core component of ABA is the use of positive reinforcement strategies to increase the probability of occurrence of certain behaviours. However, there is ongoing debate over the use of behavioural interventions as best practice for ASD. In this book , the efficacy of an ABA-based intervention was evaluated in ten children with ASD. The results of the present study demonstrated clear collateral gains in speech and social communicative behaviours. Additionally, there were significant reductions in the frequency of problem behaviours, which were associated with decreased parental stress level scores. These results indicate that ABA could be used as a tool to successfully promote target behaviours as well as reduce maladaptive behaviours in ASD.