Recent debates on sustainable development increasingly shift the focus from the technocratic and economic fix of environmental problems to more fundamental changes in socio-political processes and relations. In this shift, experts consider participation to be a genuinely transformative approach to sustainable development. Yet, the process by which this transformation takes place as an outcome of the participation is not sufficiently understood. This book considers how the act of participating in development projects can bring about social transformation that is considered to be fair and just by the participants and non-participants in a broader societal context. Drawing on ideas from social theory, anthropology and political ecology, the author proposes a reflexivity-based framework to analyse participation as a type of social action underpinned by primary experience, which can have a transformative effect if the participants are allowed to reflect on the experience, share the reflection with others through collective deliberation and interaction, and open new space for change. Social transformation cannot be planned beforehand but the conditions for it emerge from the project process, with reference to, but outside the pre-determined logical framework. Institutionalising the transformation to reshape governance needs to recognise the emerging conditions by which the participants keep on defining own terms of engagement. Using the reflexivity-based framework, the book reassesses participatory projects for sustainable development in the Amazon, an African slum, and disaster stricken areas in Japan. These cases illustrate various patterns of potentially transformative process, waiting to be appreciated by experts and policy-makers.