Tourism takes place in the environment, which is made up of both human and natural features. The human environment comprises economic, social and cultural factors and processes. The natural environment is made up of plants and animals in their habitat. It is possible to make a distinction between the human environment and the natural environment, and this is particularly useful when discussing the impacts of tourism. However, it is important to note that, in a real setting, the human environment and the natural environment are interwoven and human activity is both affected by and has effects on the natural environment. This chapter presents and discusses the key questions that need to be asked in order to understand the impacts of tourism: who, what, where, when and for how long?