Ph.D. (Educational Psychology) / The researcher explored and described principals’ management of union members’ aggression in schools. The overarching aim was to assist principals who experience aggression from union members in the schools they head. To accomplish this, the researcher developed, implemented and evaluated a psycho-educational programme to manage union members’ aggression through the facilitation of their mental health. Union members’ aggressive behaviour and attitudes have become the order of the day in schools. This hampers the quality of teaching and learning, and also contributes to the increased levels of stress and frustration for principals, who are the school managers. Notwithstanding the traumatic environment in the workplace, principals are still expected by the Gauteng Department of Education (GDE) as well as the community, to fulfil their day-to-day functions: Principals impute violence and aggression as foremost reasons why schools have become dysfunctional and ungovernable. The research design was structured into four chronological research phases. Phase One: the situation analysis was conducted according to a qualitative research approach through individual phenomenological interviews with a purposive sample of school principals. Tesch’s descriptive approach to data reduction was applied. Thereafter a literature control was conducted. Trustworthiness was ensured through adherence to credibility, transferability, dependability and confirmability...