Progressing sustainability requires a more networked approach to governance—an approach that connects otherwise segmented policy areas and fosters greater communication among governments, stakeholders and citizens. Of particular importance is the development of discursive spaces in which diverse actors are able to explore the differing knowledge, perspectives and values raised by the challenge of sustainability. This thesis develops the notion of transactional space to bring into focus the processes of reflection, dialogue and mutual learning that effective sustainability discourse involves. In the first part of the thesis I review literature on the theory and practice of participation, deliberation and collaboration, giving particular attention to the ways in which these processes have potential to create space for a depth of exchange and enable participants to engage with the tensions inherent in complex policy issues. While many authors point to the importance of negotiating difference in these processes, the literature reveals that, in practice, this type of exchange tends to be overlooked or underdeveloped. I therefore argue in this thesis that critical, reflective dialogue plays a key role in generating greater understanding among participants, more comprehensive understanding of policy issues, and more integrative and shared approaches, and for these reasons must be actively developed. The case study in the second part of the thesis explores this concern for developing reflective exchange in practice. The formation of the Western Australian Collaboration in 2002—a partnership of non-government organizations from a range of social and environmental perspectives committed to ‘a just and sustainable Western Australia’—represented an opportunity to examine the development of participatory and collaborative processes for sustainability. The thesis presents a case study of the WA Collaboration’s development over 2002-2006 to illustrate the potential such networks and open forums offer for transformative exchange around sustainability. It describes the intensive process conducted with the Steering Committee to cultivate a culture of reflection and learning in the organization, and the practical initiatives the process helped to generate. The thesis concludes with a discussion of the lessons learnt and key principles and practical considerations relevant to fostering transactional space. The WA Collaboration experience and the review of literature reveal a tendency in practice to privilege action and outcomes over reflection and learning. Furthermore, despite the necessity for a depth of engagement with complex policy issues, funding systems and policy environments often fail to allow the time and resources needed to support genuine dialogue and collaborative work. The thesis provides the concept and principles of transactional space as a means of helping to address this imbalance. They are designed to encourage practitioners to create opportunities for critical, reflective dialogue in a range of deliberative settings.