A land defender, land protector, or environmental defender is an activist who works to protect ecosystems and the human right to a safe, healthy environment. Often, defenders are members of Indigenous communities who are protecting property rights of ancestral lands in the face of expropriation, pollution, depletion, or destruction. Land and its resources may be considered sacred by Indigenous peoples, and caring for land is considered a duty that honors ancestors, current peoples, and future generations.

Land defenders face severe persecution from powerful political and corporate alliances that profit from resource extraction. which in turn may cause pollution. The United Nations Human Rights Council determined that land defenders are "among the human rights defenders who are most exposed and at risk."

During the 2016 Dakota Access Pipeline protests, members of the Standing Rock Sioux Reservation blocked the construction of the pipeline to protect the tribe's land and water supply. This grassroots effort led to hundreds of arrests and clashes with the police and National Guard soldiers. Negative articles described the Indigenous land defenders as "protesters," a term denounced by many environmental activists.

Environmental activist and actor Dallas Goldtooth of the Indigenous Environmental Network has criticized the term "protester," stating the word "protester" is negative and implies that Native people are angry, violent, or overprotective of resources.

Instead, members of the movement refer to themselves as "land defenders," a term that emphasizes pacifism and responsibility to care for ancestral lands which may be part of the defender's heritage.

Inuit Labrador land protector Denise Cole has stated, "I am very much a believer when I take my medicines, when I take my drum, what colonial law would call protesting is very much what I consider is ceremony."

Land defenders play an active and increasingly visible role in actions intended to protect, honour, and make visible the importance of land. There are strong connections between the water protector movement, land defender movement, and Indigenous environmental activism. Land defenders resist the installation of pipelines, fossil fuel industries, the destruction of territory for development such as agriculture or housing, and resource extraction activities such as fracking because these actions can lead to the degradation of land, destruction of forest, and disruption of habitat. Land defenders resist activities that harm land, especially across Indigenous territories and their work is tied to human rights. Yazzie points to the resistance tactics of Diné land defenders and their anti-capitalist and anti-development stance on resource extraction as being highly connected to the longstanding traditions of Diné resistance.

Activism can come in the form of the erection of blockades on reserve lands or traditional territories to block corporations from resource extraction activities. Water and land protectors also erect camps as a way to occupy traditional territories and strengthen cultural ties. Land defenders also work through legal frameworks such as government court systems in effort to keep control of traditional territories. Civil disobedience actions taken by land defenders, are frequently criminalized and some have argued subject to heavier policing and violence.