Assessment of children's restricted and repetitive behaviours offers potential opportunities to improve early diagnosis of autism spectrum disorder (ASD) and timely access to interventions and support. To facilitate this requires understanding of the phenomenology of repetitive behaviours in ASD, including differentiating behaviours seen in ASD from other populations such as young typically developing and developmentally delayed children. A key factor in achieving understanding is valid and reliable measurement. This review considers the issues in conceptualisation of repetitive behaviours which should guide the choice of measurement tool, including definition of subtypes of repetitive behaviours, associations with age and ability, and categorisation of frequency and severity. The resulting conclusions about the requirements for measurement are applied within a systematic review of quantitative interview and questionnaire measures of repetitive behaviour used with children with ASD. The conclusions of the review lead to recommendations for existing and future research on restricted and repetitive behaviours in ASD. (Contains 1 table.)