Sustainability education is a contested field in Aotearoa New Zealand, as it is in other countries. A variety of philosophical and theoretical interpretations and possibilities for practice therefore co-exist within this emerging field. This thesis develops a ‘complex perspective’ of sustainability education by exploring the way it is conceptualised in literature and the New Zealand curriculum, and interpreted in practice in the context of a New Zealand secondary school. Guided by the key contributing theories and a qualitative methodology, the thesis maps the complexity of the field from the macro- or global and international level to the micro- or local level using the reference points of theory, practice, and possibility. Developed during and in response to an intense period of social and environmental change that shows no signs of abating, the thesis comprises two interrelated components. The first and more substantial component is the literature review. This takes account of situational factors that are giving rise to different conceptions and approaches to sustainability education and to contrasting views presented in literature and curriculum. Used as an umbrella term for all forms of education with environmental and sustainability foci, ‘sustainability education’ (in whatever form it takes) stands as an admission of broad social failure and the need for substantial change. Conceptions of sustainability education range from ‘education for sustainable development’ (ESD), which is advanced by the United Nations and other influential international organisations, to ‘education for sustainability’ (EfS), which has taken precedence over ‘environmental education’ (EE) in the New Zealand curriculum. The literature shows that this complex, contested, contextualised and emerging field is as much hopeful as it is critical. The qualitative case study comprises the second interrelated component of the thesis. Grounded in the real-life context of a secondary school with a distinctive approach to teaching and learning, it involves an empirical investigation of the ways in which two teachers and a diverse group of Year 9 to Year 14 students understand and practice sustainability education. This component draws on the interpretive methods of interviewing and observation to afford an empathetic and multi-perspectival view of sustainability education in practice. The case does not strive to establish ‘truth’ but rather to be open to multiple truths, realities and meanings - in a manner that is consistent with the theories of social constructionism and interpretivism in particular. It is suggested, through this study, that sustainability education cannot be confined to a stable conception or consistent framework, or approached through a programme of standardised levels and assessments. Representing a complex, multi-dimensional, dynamic and emergent concept, sustainability education may best be approached and sustained in a corresponding fashion, through multiple, critically-informed, and dialogically-linked points of entry.