Protected areas worldwide are becoming more and more crowded, with more and more people visiting them for more and more different activities. This applies to all types of protected areas, but particularly to JUCN Category 11 areas, referred to here as national parks, or simply parks. Visitors include private individuals, non-profit groups and commercial tour clients. Global demand for nature and adventure tourism and recreation continues to grow, and parks provide one of the main opportunities. Parks agencies now have to devote a considerable proportion of their time and resources to visitor management; often, much more than they can now devote to conservation management. Their research and information needs have changed accordingly. The same applies for other public and private owners and managers of land with high recreational use. In parks with low visitation, the major monitoring requirements relate to external environmental threats, such as: weeds and feral animals entering the park from neighboring properties and becoming established; unscheduled fires; outbreaks of plant or animal diseases; illegal human activities, such as poaching, logging or seed collecting; and air or water pollution in the park from external sources upwind or upstream. In parks and other land with high levels of visitation, land managers also need information on visitor characteristics, visitor impacts and the effectiveness of visitor management tools. Visitor characteristics may include numbers, origins, activities, expectations and satisfaction, and are determined principally from on-site visitor surveys, sometimes coupled with automatic counters and similar approaches. The effectiveness of visitor management tools can be assessed both in terms of increased visitor satisfaction, and reduced visitor impacts.