Good indications as to the incidence rates concerning bullying, aggressive behaviour and violence in schools have been developed both in Ireland and internationally. This book presents and discusses a study of 2,794 students from eight post-primary schools in the Republic of Ireland who completed a specially-designed 38-item questionnaire, administered according to standardised instructions by class teachers in normal school time. Across the sample, around one in seven students reported having been cyber-bullied over the past couple of months, and around one in eleven reported having taken part in the cyber-bullying of others at school within the past couple of months. This research study confirms that the incidence of cyber-bullying amongst post-primary students in schools in Ireland is significant, and that its seriousness as an issue should not be underestimated.