Rewilding is a form of ecological restoration aimed at increasing biodiversity and restoring natural processes. It differs from other forms of ecological restoration in that rewilding aspires to reduce human influence on ecosystems. It is also distinct from other forms of restoration in that, while it places emphasis on recovering geographically specific sets of ecological interactions and functions that would have maintained ecosystems prior to human influence, rewilding is open to novel or emerging ecosystems which encompass new species and new interactions.

A key feature of rewilding is its focus on replacing human interventions with natural processes. Rewilding enables the return of intact, large mammal assemblages, to promote the restoration of trophic networks. This mechanism of rewilding is a process of restoring natural processes by introducing or re-introducing large mammals to promote resilient, self-regulating, and self-sustaining ecosystems. Large mammals can influence ecosystems by altering biogeochemical pathways as they contribute to unique ecological roles, they are landscape engineers that aid in shaping the structure and composition of natural habitats. Rewilding projects are often part of programs for habitat restoration and conservation biology, and should be based on sound socio-ecological theory and evidence.

While rewilding initiatives can be controversial, the United Nations has listed rewilding as one of several methods needed to achieve massive scale restoration of natural ecosystems, which they say must be accomplished by 2030 as part of the 30x30 campaign.

The term rewilding was coined by members of the grassroots network Earth First!, first appearing in print in 1990. It was refined and grounded in a scientific context in a paper published in 1998 by conservation biologists Michael Soulé and Reed Noss. Soulé and Noss envisaged rewilding as a conservation method based on the concept of 'cores, corridors, and carnivores'. The key components of rewilding incorporate large core protected areas, keystone species, and ecological connectivity based on the theory that large predators play regulatory roles in ecosystems. '3Cs' rewilding therefore relied on protecting 'core' areas of wild land, linked together by 'corridors' allowing passage for 'carnivores' to move around the landscape and perform their functional role. Inside these cores, human development, especially the building of roads, is strictly limited. National parks and wilderness reserves are the most common types of 'core' areas. Soulé and fellow biologist John Terbough expanded on the concept of corridors in their book Continental Conservation. They determined that one size does not fit all: narrow, linear corridors might work for some smaller species, but if conservationists wanted to encourage the movement of large carnivores, they needed to make corridors wide enough to allow for daily and seasonal movement of both herds of prey and packs of their predators. The '3Cs' concept was developed further in 1999 and Earth First co-founder, Dave Foreman, subsequently wrote a full-length book on rewilding as a conservation strategy.

Rewilding was developed as a method to preserve functional ecosystems and reduce biodiversity loss, incorporating research in island biogeography and the ecological role of large carnivores. In 1967, The Theory of Island Biogeography by Robert H. MacArthur and Edward O. Wilson established the importance of considering the size and fragmentation of wildlife conservation areas, stating that protected species and areas remained vulnerable to extinctions if populations were small and isolated. In 1987, William D. Newmark's study of extinctions in national parks in North America added weight to the theory. The publications intensified debates on conservation approaches. With the creation of the Society for Conservation Biology in 1985, conservationists began to focus on reducing habitat loss and fragmentation.

Supporters of rewilding initiatives range from individuals, small land owners, local non-governmental organizations and authorities, to national governments and international non-governmental organizations such as the International Union for Conservation of Nature. While rewilding efforts can be well regarded, the increased popularity of rewilding has generated controversy, especially in relation to large-scale projects. These have sometimes attracted criticism from academics and practicing conservationists, as well as government officials and business people. Nonetheless, a 2021 report for the launch of the UN Decade on Ecosystem Restoration, the United Nations listed rewilding as one of several restoration methods which they state should be used for ecosystem restoration of over 1 billion hectares.

Since its origin, the term rewilding has been used as a signifier of particular forms of ecological restoration projects that have ranged widely in scope and geographic application. In 2021 the journal Conservation Biology published a paper by 33 coauthors from around the world. Titled 'Guiding Principles for Rewilding', researchers and project leaders from North America (Canada, Mexico and the United States) joined with counterparts in Europe (Denmark, France, Hungary, The Netherlands, Switzerland, and the UK), China, and South America (Chile and Colombia) to produce a unifying description, along with a set of ten guiding principles.

The group wrote, 'Commonalities in the concept of rewilding lie in its aims, whereas differences lie in the methods used, which include land protection, connectivity conservation, removing human infrastructure, and species reintroduction or taxon replacement.' Referring to the span of project types they stated, 'Rewilding now incorporates a variety of concepts, including Pleistocene megafauna replacement, taxon replacement, species reintroductions, retrobreeding, release of captive-bred animals, land abandonment, and spontaneous rewilding.'