There are three aspects of the emerging urban environment that must be considered. First, urban areas constitute a unique, densely populated habitat that is environmentally distinct from non-urban settings and, by virtue of its scale, distinct from urban settings in the past. Second, urban areas exert significant environmental impacts on their immediate surroundings, their hinterlands, and the regions of which they are a part. Third, the largest urban areas are frequently linked by transportation, trade, and population migration in an interacting system of global cities. Within this system, economic, demographic, and political decisions influence not only the local environment, but also the environments of distant regions. We will examine each of these three components of the urban environment.