Action research changes people's practices, their understandings of their practices, and the conditions under which they practise. It changes people's patterns of 'saying', 'doing' and 'relating' to form new patterns ' new ways of life. It is a meta-practice: a practice that changes other practices. It transforms the sayings, doings and relatings that compose those other practices. Action research is also a practice, composed of sayings, doings and relatings. Different kinds of action research ' technical, practical and critical ' are composed in different patterns of saying, doing and relating, as different ways of life. This paper suggests that 'Education for Sustainability', as an educational movement within the worldwide social movement responding to global warming, may be a paradigm example of critical action research.