This master‟s thesis is about cyber-bullying prevention in primary school. My reason for choosing this issue was a desire to get a greater insight into cyber-bullying as a phenomenon. In addition, I found it interesting to find how the principals can work systematically for prevention and reduction of cyber-bullying incidents in schools, with the purpose of offering pupils a good psycho-social environment as enshrined in the Education Act, Section 9a-3. My attention was focused on understanding the concept cyber-bullying, cyber-bullying prevention measures, and challenges in cyber-bullying prevention. Before the interview, a literature review was performed. In this study, I used the qualitative semi-structured interview together with Grounded Theory approach. Specific selection criteria were used to select respondents for the survey. Four informants were interviewed. A bilingual interview guide was prepared in advance of the interviews. The questions for the interview guide were based on the following main issues and research questions: How do Norwegian principals reflect upon cyber-bullying prevention? 1. How do primary principals understand the concept cyber-bullying? 2. Which of the preventive measures that are used against cyber-bullying in primary school are considered by principals to be effective? 3. What kind of challenges do primary school principals experience as regards implementing preventive measures against cyber-bullying? The following conclusions were arrived at: Cyber-bullying prevention in the framework of the unwanted behavior prevention can be considered effective in the Norwegian context. Such prevention should be based on the principles of positive attitudes and proactive development, proactive development of responsibility for own behavior, emphasizing the positive behavior and providing predictable responses to negative behavior and proactive empathy training. The process of the theory development is illustrated.