The rapid increase in popularity of mass tourism has raised a series of concerns about how far present levels of such activity can be sustained. One key problem is that tourism is a private sector activity in which participating firms are motivated by profit. Left to their own devices, firms in the leisure and tourism industry tend to make their output decisions around considerations of profit, with little or no regard for the social costs of their activities. One result can be, for example, a straggling assortment of ugly hotel and leisure developments, traffic congestion and pollution in various forms.