The Chernobyl Nuclear Power Plant Zone of Alienation, also called the 30-Kilometre Zone or simply The Zone, was established shortly after the 1986 Chernobyl disaster in the Ukrainian SSR of the Soviet Union.

Initially, Soviet authorities declared an exclusion zone spanning a 30-kilometre (19 mi) radius around the Chernobyl Nuclear Power Plant, designating the area for evacuations and placing it under military control. Its borders have since been altered to cover a larger area of Ukraine: it includes the northernmost part of Vyshhorod Raion in Kyiv Oblast, and also adjoins the Polesie State Radioecological Reserve in neighbouring Belarus. The Chernobyl exclusion zone is managed by an agency of the State Emergency Service of Ukraine, while the power plant and its sarcophagus and the New Safe Confinement are administered separately.

The current area of approximately 2,600 km² (1,000 sq mi) in Ukraine is where radioactive contamination is the highest, and public access and habitation are accordingly restricted. Other areas of compulsory resettlement and voluntary relocation not part of the restricted exclusion zone exist in the surrounding areas and throughout Ukraine. In February 2019, it was revealed that talks were underway to re-adjust the exclusion zone's boundaries to reflect the declining radioactivity of its outer areas.

Public access to the exclusion zone is restricted in order to prevent access to hazardous areas, reduce the spread of radiological contamination, and conduct radiological and ecological monitoring activities. Today, the Chernobyl exclusion zone is one of the most radioactively contaminated areas on Earth and draws significant scientific interest for the high levels of radiation exposure in the environment, as well as increasing interest from disaster tourists. It has become a thriving sanctuary, with natural flora and fauna and some of the highest biodiversity and thickest forests in all of Ukraine, due primarily to the lack of human activity in the exclusion zone since 1986.

Since the beginning of the Russian invasion of Ukraine in February 2022, the Chernobyl exclusion zone has been the site of fighting with neighbouring Russia, which captured Chernobyl on 24 February 2022. By April 2022, however, as the Kyiv offensive failed, the Russian military withdrew from the region. Ukrainian authorities have continued to keep the exclusion zone closed to tourists, pending the eventual cessation of hostilities in the Russo-Ukrainian War.

Historically and geographically, the zone is the heartland of the Polesia region. This predominantly rural woodland and marshland area was once home to 120,000 people living in the cities of Chernobyl and Pripyat as well as 187 smaller communities, but is now mostly uninhabited. All settlements remain designated on geographic maps but marked as нежил. (nezhyl.) – "uninhabited". The woodland in the area around Pripyat was a focal point of partisan resistance during the Second World War, which allowed evacuated residents to evade guards and return into the woods. In the woodland near the Chernobyl Nuclear Power Plant stood the "Partisan's Tree" or "Cross Tree", which was used to hang captured partisans. The tree fell down due to age in 1996 and a memorial now stands at its location.

The Exclusion Zone was established on 2 May 1986 (1986-05-02) soon after the Chernobyl disaster, when a Soviet government commission headed by Nikolai Ryzhkov decided on a "rather arbitrary" area of a 30-kilometre (19 mi) radius from Reactor 4 as the designated evacuation area. The 30 km Zone was initially divided into three subzones: the area immediately adjacent to Reactor 4, an area of approximately 10 km (6 mi) radius from the reactor, and the remaining 30 km zone. Protective clothing and available facilities varied between these subzones.

Later in 1986, after updated maps of the contaminated areas were produced, the zone was split into three areas to designate further evacuation areas based on the revised dose limit of 100 mSv.