A demilitarized zone, DMZ or DZ is an area in which treaties or agreements between nations, military powers or contending groups forbid military installations, activities or personnel. A DMZ often lies along an established frontier or boundary between two or more military powers or alliances. A DMZ may sometimes form a de facto international border, such as the 38th parallel between North and South Korea. Other examples of demilitarized zones are a 120-mile (190 km) area between Iraq and Kuwait, Antarctica (preserved for scientific exploration and study) and outer space (space more than 100 miles (160 km) from the earth's surface).

Many demilitarized zones are considered neutral territory because neither side is allowed to control it, even for non-combat administration. Some zones remain demilitarized after an agreement has awarded control to a state which (under the DMZ terms) had originally ceded its right to maintain military forces in the disputed territory. It is also possible for powers to agree on the demilitarization of a zone without formally settling their respective territorial claims, enabling the dispute to be resolved by peaceful means such as diplomatic dialogue or an international court.

Several demilitarized zones have also unintentionally become wildlife preserves because their land is unsafe for construction or less exposed to human disturbances (including hunting). Examples include the Korean Demilitarized Zone, the Vietnamese Demilitarized Zone, and the Green Line in Cyprus.