The quality of the environment is a key tourism resource. No matter what the short- or medium-term economic benefits of tourism development appear to be, tourism cannot be sustained at the optimal level if the environmental resource base is degraded beyond a threshold capacity. An understanding of the potentially very complex relationship between tourism development and the maintenance of environmental quality is crucial to the success of tourism projects, programmes and policies. This chapter reviews the previous research concerned with tourism and the environment, particularly that relating to environmental impacts. It emphasizes the importance of the environment as a tourism resource before going on to discuss the importance of, and methodological issues raised by, the assessment of environmental impacts. The chapter concludes with a discussion of the application of the Delphi technique to environmental impact assessment (EIA). Tourism projects, it is argued, should be subject to EIA in order to ensure that, in the interests of their long-term success, they do not cause unforeseen and unacceptable environmental degradation. Ensuring that EIA procedures and methods are made as efficient as possible will involve continued research into 'scoping' techniques for rapid critical appraisal, the use of qualitative judgements by the local community and the integration of economic and environmental considerations, among other issues.