"Transformative leaders for sustainable schools", was a nationwide research project conducted in 150 primary schools in Cyprus during 2005-2007. The project explored the role of the principals in the organisation of sustainable schools. A mixed methods approach to data collection was employed combining quantitative and qualitative methods. This paper presents primary school principals' perceptions of sustainable development, their views on the characteristics and operation of the sustainable schools as well as factors supporting or impeding the development of such schools in Cyprus. Our analysis reveals that the term "sustainable school" is a concept only vaguely understood by the principals. Education for sustainable development is interpreted loosely as environmental education and sustainable schools' operation is limited to sustainable development's environmental aspects. Principals place their emphasis on environmental conservation, for satisfying humans' needs whereas the notion of environment, economy and society are marginalised. The development of sustainable schools in Cyprus is restricted by limitations in time, lack of ESD teacher education, the centralised educational system and the overloaded curriculum. Suggested reinforcing factors are parents' associations' support and the school-community dialogue. Further exploration of the principals' role as potential carriers of change and effective leaders is needed. (Contains 5 tables.)