China's quest for sustainable development has given birth to a set of contested ‘ecological construction’ programmes. Focusing on ‘ecological resettlement’, a type of policy measure in a programme for restoring degraded grasslands, this thesis sets out a critical analysis in opposition to the dominant technical and managerial approaches to understanding environmentalisation. The aim is to draw out the politics of the formulation, implementation and effects of ecological resettlement at and across different scales. The study combines fieldwork, interviews, analysis of policy documents, and statistical analysis while theoretically, in addition to political ecology, it incorporates concepts and models from environmental governance, migration, and pastoralism studies. Environmentalisation is examined through three types of analysis: environmentalisation of the state, reshaping of state-society relations, and (re)territorialisation. A central theme is how local processes are linked to national considerations and how the local state acts as an intermediary between the central state and the pastoralists. The analysis exposes the practices that enabled the central state to define the problem of grasslands and devise interventions, illustrating the environmentalisation of the state. However, at the local level, incentives and interests defined by the political structure drove the developmental local state to pursue short-term-effective rather than sustainable practices. On the other hand, while the pastoral households responded to the projects with different strategies, their migration decisions suggested that social, economic and cultural considerations played a more important role than environmental concerns. Moreover, ecological resettlement has led to a significant change of Mongolian pastoralism. Land-tenure-based management further fragmented rangelands while the emergence of new social arrangements enabled migrant households to remain involved with pastoralism.