The most critical aspect of sustainability in the tourism industry is through its links to conservation. Environmental aspects of urban tourism can be managed adequately through building regulations and transport systems, and environmental planning, impact assessment and pollution control processes. It is outdoor tourism in areas of high conservation value where marginal differences in management have the greatest effects on the natural environment, through a variety of direct and indirect mechanisms. Turnover in the outdoor tourism sector worldwide has been estimated at around US$1 trillion annually, which gives the sector considerable economic and political power to influence conservation in either a positive or negative way. Many governments put tourism and conservation in the same ministerial portfolios, and tourism industry associations lobby to gain greater control over protected area agencies and estates. This chapter therefore focuses principally on outdoor tourism and its implications for conservation, acknowledging the importance of international travel and cultural differences.