This chapter discusses the beaver’s role as a keystone species, wetland engineers and riparian restorers. Beavers can have a significant impact on the natural landscape, the geomorphology and hydrology of a system and biodiversity, as a result of their activities. Beaver-influenced environments, with a less dense or intermittent tree canopy, provide both a greater expanse and increased variety of living opportunities for a wide range of higher plant species, which in turn increases the feeding and breeding opportunities for insects. A greater abundance of standing and submerged dead wood habitat further enhances this process, and invertebrate densities can alter significantly in response. The presence of beavers thus tends to have a beneficial impact on fish populations through the creation of foraging and shelter habitats for a wide variety of species. Amphibian abundance in beaver-generated landscapes tends to be higher than in areas without beavers, and this has also generally been found to be true for reptiles and birds. Small mammals (such as water shrews and voles) adapt to utilize the variety of niche habitats and prey abundance provided by beaver-generated landscapes, while large herbivores such as deer exploit their greater grazing and browsing potential. Carnivores, particularly otter and mink but also potentially badger, red fox, stoat, and pine marten, may benefit through enhanced prey populations (such as fish, amphibians, and birds) and the presence of beaver lodges and burrows which they utilize for shelter and breeding.