This thesis explores how Education for Sustainable Development (ESD) as an overarching perspective makes meaningof educational aims and purposes. Sustainable development, as a concept, is by necessity complex, and deals withintegrated dimensions of environmental, social-cultural and economic sustainability. It involves a diverse range ofembedded values and ideologies and calls for engagement in value-related and political issues relating to environment,equality and lifestyle. In my thesis, I have turned to the actors in social practice who are set to realise the educationalperspectives of ESD – the teachers. Accordingly, the analyses departure from secondary and upper secondary schoolteachers’ reciprocal meaning-making when discussing the desirable aims of teaching and ESD. Building upon previouseducational research, the thesis has three purposes, and the results are presented in four articles. The results of thestudies bring new empirical knowledge and perspectives to educational research and practice, by adding furtherunderstanding of the political and democratic dimensions of ESD.The first purpose is to investigate and describe the complexity of the concept of sustainable development from a conflictperspective and to analyse meaning-making discussions of sustainability in an educational context. This is elaborated inthe first study (Article I). To achieve this, a Conflict Reflection Tool (CRT) has been developed, by combining theconflicting dynamics of sustainable development with dialogic and univocal functions of speech. In the included casestudy, the CRT analysis of teachers’ discussions shows how fact-based, univocal science utterances closed thediscussion for conflicting perspectives to emerge. However, conflicting views did emerge and were re-valued in adialogic genre through the interplay of different dimensions of sustainability and different societal levels of conflicts.The second purpose is to investigate how the desired aims of ESD are (re)articulated in areas of educational tension inorder to make particular meaning by teachers with experience in ESD practice. Three complex ESD areas are in focus,namely, the development of students as political subjects (Article II), qualification in relation to ESD (Article III), andeducation for social change in relation to ‘sustainable’ living (Article IV). In each of these areas, the functions ofqualification, socialisation and subjectification (c.f. Biesta) are relationally analysed to further problematise educationalpurposes. Through analyses with inpiration from discourse theory, the results show in Article II the emerging discourse ofcritical thinking as room for subjectification where students were invited to be adressed as political subjects. This discoursewas articulated in struggle with the aims of qualification and socialisation, i.e. challenged by elements articulating a morescientific and rational worldview. Article III shows three discourses of qualification. Of these three, scientific reasoningand awareness of complexity are articulated as contrasting epistemological discourses of qualification. However, in thethird discourse, qualification as critical thinking, these different epistemological views are articulated as intertwined asdifferent ways to view sustainability. Article IV shows how the teachers struggle between three positions: the rationalsubject, as a neutral conductor; the responsible subject, as a role model, or the reconstructing subject, as a reconstructor.The overlapping positions depend upon how socialisation towards sustainable lifestyles, political and ethical perspectivesare identified in relation to the educational aims and the emerging myths of social change.The third purpose is to develop analytical methods where conflicting articulations of environmental issues andsustainability are taken into account based on language and discourse theory for conducting empirical investigations ofmeaning-making.