War can heavily damage the environment, and warring countries often place operational requirements ahead of environmental concerns for the duration of the war. Some international law is designed to limit this environmental harm.

War and military activities have obvious detrimental impacts on the environment. Weaponry, troop movements, land mines, creation and destruction of buildings, destruction of forests by defoliation or general military usage, poisoning of water sources, target-shooting of animals for practice, consumption of endangered species out of desperation etc., are just some of the examples of how both war and peacetime military activities (such as training, base construction, and transportation of weaponry) harm the environment. "Scorched earth" and "poisoning the well" are classical examples of such impact. Recent examples include the oil dump and fire by Iraq in Kuwait 1990/1991, depleted uranium use in Kosovo 1999, air fuel explosives use in Afghanistan since 2001.

From a legal standpoint, environmental protection during times of war and military activities is addressed partially by international environmental law. Further sources are also found in areas of law such as general international law, the laws of war, human rights law and local laws of each affected country. However, this article is chiefly focused on the environment and as soon as two countries are battling it out, the issue becomes one of international concern. Thus, international environmental law that the United Nations Security Council enforces is the focus here. The law of armed conflict is not very well developed in comparison to other areas of international law. Only the United Nations Security Council has the authority and the jurisdiction to regulate its development and implementation, or to monitor its observance.

Customary international law and soft law documents address the protection of the environment during times of armed conflict and military activities. The International Law Commission (ILC) has drafted a Code of Offences Against the Peace and Security of Mankind (1954).

"Man and his environment must be spared the effects of nuclear weapons and all other means of mass destruction. States must strive to reach prompt agreement, in the relevant international organs, on the elimination and complete destruction of such weapons": Principle 26 of the 1972 Stockholm Declaration → Chapter 11 of the Brundtland Report: Peace, Security, Development, and the Environment. World Charter of Nature 1982: "Nature shall be secured against degradation caused by warfare or other hostile activities."

"Warfare is inherently destructive of sustainable development. States shall therefore respect international law providing protection for the environment in times of armed conflict and cooperate in its further development, as necessary": Principle 24 1992 Rio Declaration → paragraph 39.6 of the Agenda 21: "measures in accordance with international law should be considered to address, in times of armed conflict, large-scale destruction of the environment that cannot be justified under international law".

UN General Assembly Resolution 47/37 (1992) provides: "[D]estruction of the environment, not justified by military necessity and carried out wantonly, is clearly contrary to existing international law."

Several United Nations treaties, including the Fourth Geneva Convention, the 1972 World Heritage Convention and the 1977 Environmental Modification Convention have provisions to limit the environmental impacts of war or military activities.