Background: Sustainable development, as an area of knowledge, appears in several different places in the curriculum and does not fit neatly within the scope of traditional subject areas. In many countries, including Sweden, it has long been upheld as an important tool for increasing understanding of, and dealing with, environmental problems. It is not clear, however, what role education can actually have in the making of a more sustainable future. Even though there are several potential ways for sustainable development to be involved in education, the concept raises many questions when transferred to the school context. Purpose: This paper investigates how teachers deal with the difficulty of defining and approaching sustainable development as an area of knowledge in Swedish schools. Sample: This article is based on semi-structured interviews with 40 teachers, 13 of whom were lower secondary school teachers (pupil age 12-15) and 27 were upper secondary school teachers (pupil age 15-18). The study involves teachers in all subjects where sustainable development is a goal in the syllabus. The study is also based on participant observation in one upper secondary class. A total of 17 different schools were involved, from a wide range of locations in Sweden. Design and methods: The paper builds on qualitative data and the analysis of transcribed interviews and group interviews with teachers in Swedish lower and upper secondary schools. Group interviews, involving three or more people, were conducted on eight occasions. The pupils at an upper secondary school were also observed while they were working on a course called 'policy and sustainable development'. Data were transcribed and analysed thematically. Findings: The analysis suggests that, according to the teachers' experiences, the demands of equivalence and measurability in school have increased and that this affects how sustainable development is approached in teaching and learning. Three main categories of knowledge were identified. The study also presents two representations that model how teachers may approach knowledge about sustainable development - metaphorically termed 'the Accountant' and 'the Adventurer' - and their different effects on knowledge. Conclusions: There is a tendency for complex knowledge areas such as sustainable development, which do not fit seamlessly into traditional curriculum subjects, to become oversimplified when translated into teaching situations. According to the representations that we described metaphorically, the teacher, as an accountant, is characterised by 'knowledge instrumentalism', which means that teachers administer knowledge and the pupils consume it. In this transactional model, the accountant is also very dependent on external governance and control. Alternatively, the teacher, as an adventurer, is characterised by authority, knowledge and self-control. In this model, knowledge sometimes grows in an unpredictable way in the meeting between people who share common experiences. For adventurers, sustainable development is a matter of commitment and awareness, and it involves an explicit stance. The metaphors can be placed on a continuum which describes how teachers manage the demands of the school system in relation to the knowledge area of sustainable development. [ABSTRACT FROM AUTHOR]