Although there has been a growing interest in research on bullying in the last decade the majority of studies have used definitions of bullying and victimisation derived from researchers' perceptions of the problem. The aim of the present study was to examine pupils' definitions of bullying in school. The participants were 166 pupils in the top two years in five primary schools in Ireland (two in urban areas and three in rural areas). There were 89 male and 77 female participants, with a modal age of 12 years. An interview was designed to elicit pupils' perceptions of the defining characteristics of bullying behaviour including (I) the behaviours described as bullying, (II) the importance of repetition, (III) the importance of intention, (IV) the effect on the victim, (V) the role of provocation and (VI) imbalance of power. The results suggest that repetition, intention, and a lack of provocation may not be central to pupils' definitions of bullying. These results indicate some differences between pupils and researchers on what constitutes the most important defining characteristics of bullying. This suggests that approaches to bullying intervention programmes may need to be reconsidered in light of these findings. (Contains 3 tables.)