Many human behaviours, including social, political, and economic actions, have an impact on the natural environment, and are responsible for causing many of the current environmental challenges and issues. This raises the importance of education, particularly environmental education (EE), as a necessary tool to equip people to address environmental issues and move towards environmental sustainability. International EE declarations such as the Tbilisi Declaration have highlighted that investigating peoples’ environmental awareness, attitudes, and behaviour towards environmental issues could inform educational approaches geared towards a more sustainable future. The research presented in this thesis explored the environmental awareness, attitudes, and behaviour of secondary school students and teachers in Tehran, Iran. The aim was to investigate the current context of EE in Iranian secondary schools. An interpretive approach was used to explore participants’ perspectives through a mix of quantitative and qualitative data, including questionnaires, individual interviews, and focus group interviews. Data were collected in six secondary schools in Tehran, the capital city of Iran. Two populations were included: 337 secondary school students (9th grade) and 12 secondary school teachers. Two different computer software programmes (SPSS for quantitative and NVivo for qualitative data) were used for data analysis and coding. The findings indicated that students had reasonably high levels of understanding about environmental issues, particularly about local issues that have a greater impact on their everyday lives, such as air pollution. This highlights the important issue of context. Students also expressed positive attitudes towards the environment, but indicated low levels of agency. Many researchers have shown that both awareness and attitudes are prerequisites of pro-environmental behaviour. However, they are not necessarily sufficient for action, as confirmed in this study. In this research, particular attention therefore focused on the complexities of Iranian students’ environmental behaviour. A low level of intention to act, along with students’ reported lack of locus of control to make changes for future of the environment, seemed to influence their relative absence of pro-environmental behaviour. The findings also indicated that teachers’ connection with nature, their life experiences, personal interests, and teaching areas are important aspects that can contribute to effective EE in Iran. However, significant barriers to the further delivery of EE in Iranian secondary schools include a relatively low level of in-depth environmental content in the curriculum, lack of outdoor education, teacher-centred approaches to classroom learning, and time pressures for teachers. This research contributes to an understanding of current issues impacting on EE in Iran, providing insights into the contextual nature of the three key aspects of EE (awareness, attitudes, behaviour) for junior secondary students and teachers. This provides an important baseline from which to further develop understanding of how to improve EE programmes in the Iranian context. The research concludes that in order to address environmental problems in Iran, a substantial shift needs to occur with respect to students’ environmental attitudes, their sense of agency, and their behaviours in order to work towards more sustainable approaches to living. Teachers need to be supported to better implement EE. This includes modifying their environmental education pedagogy towards a more student-centred approach of teaching. In order to do this, the internal and external obstacles described in this thesis will need to be addressed to help Iran develop more environmentally sustainable approaches to the future.