Białowieża Forest is a large forest complex on the border between Poland and Belarus. It is one of the last and the largest remaining part of the immense primeval forest that once stretched across the European Plain. The forest is home to more than 800 European bisons, Europe's heaviest land animal. UNESCO's Man and the Biosphere Programme designated the Polish Biosphere Reserve Białowieża in 1976 and the Belarusian Biosphere Reserve Biełavieskaja pušča in 1993.

In 2015, the Belarusian Biosphere Reserve spanned 216,200 ha (2,162 km; 835 sq mi), subdivided into transition, buffer and core zones. The forest has been designated a UNESCO World Heritage Site and an EU Natura 2000 Special Area of Conservation. The World Heritage Committee, through its decision of June 2014, approved the extension of the UNESCO World Heritage site "Belovezhskaya Pushcha / Białowieża Forest, Belarus, Poland", which became "Białowieża Forest, Belarus, Poland". It straddles the border between Podlachia historical region in Poland and Brest and Grodno Oblasts in Belarus, and is 62 kilometres (39 miles) southeast of Białystok, Poland and 70 kilometres (43 miles) north of Brest, Belarus. The Białowieża Forest World Heritage site covers a total area of 141,885 ha (1,418.85 km; 547.82 sq mi). Since the border between the two countries runs through the forest, there is a border crossing available for hikers and cyclists.

The Białowieża Forest takes its name from the Polish village of Białowieża, which is located in the middle of the forest and was probably one of the first human settlements in the area. Białowieża means "White Tower" in Polish. The name stems from the white wooden hunting-manor established in the village by Władysław II Jagiełło, the Grand Duke of Lithuania and later King of Poland who enjoyed going on hunting trips in the forest, which was then part of the Grand Duchy of Lithuania. The modern Belarusian name for the forest is Biełaviežskaja pušča (Белавежская пушча), although both the Belarusian authorities and UNESCO use the official Russian name Belovezhskaya pushcha (Беловежская пуща) from before the 1991 dissolution of the Soviet Union.

On the Polish side, part of the Białowieża Forest is protected as the Białowieża National Park (Polish: Białowieski Park Narodowy), with an area of about 105 km (41 sq mi). There is also the Białowieża Glade (Polish: Polana Białowieska), with a complex of buildings once owned by the tsars of Russia during the Partitions of Poland. At present, a hotel and restaurant with a car park is located there. Guided tours into the strictly protected areas of the park can be arranged on foot, bike or by horse-drawn carriage. Approximately 120,000–150,000 tourists visit the Polish part of the forest annually (about 10,000 of them are from other countries). Among the attractions are birdwatching with local ornithologists, the chance to observe rare birds, pygmy owl observations, watching bison in their natural environment, and sledge as well as carriage rides, with a bonfire. Expert nature guides can also be found in the nearby urban centres. Tours are possible all year round. The popular village of Białowieża lies within the forest. Białowieża means "the white tower" in Old Polish.

On the Belarusian side, the forest is protected as the Belavezhskaya Pushcha National Park with an area of 1,771 km (684 sq mi). The core, strictly protected, area covers 38%, the zone of regulated use 26,1%, and the touristic zone and economic zone combined 36%; the National Park and World Heritage Site comprises 876 km (338 sq mi). The Belovezhskaya pushcha headquarters at Kamieniuki include laboratory facilities and a zoo where European bison (reintroduced into the park in 1929), konik (a semi-wild horse), wild boar, Eurasian elk and other indigenous animals may be viewed in enclosures of their natural habitat. A new attraction there is a New Year's museum with Ded Moroz (the East Slavic counterpart of Father Christmas).

The entire area of northeastern Europe was originally covered by ancient woodland similar to that of the Białowieża Forest. Until about the 14th century, travel through the woodland was limited to river routes; roads and bridges appeared much later. Limited hunting rights were granted throughout the forest in the 14th century. In the 15th century the forest became a property of Grand Duke Jogaila. A wooden manor in Białowieża became his refuge during a plague pandemic in 1426. The first recorded piece of legislation on the protection of the forest dates to 1538, when a document issued by Sigismund I instituted the death penalty for poaching a bison. The King also built a new wooden hunting manor in a village of Białowieża, which became the namesake for the whole complex. Since Białowieża means the "white tower", the corresponding Puszcza Białowieska translates as the "forest of the white tower". The Tower of Kamyenyets on the Belarusian side, built of red brick, is also referred to as the White Tower (Belaya Vezha) even though it was never white, perhaps taking the name from the pushcha.

The forest was declared a hunting reserve in 1541 to protect bison. In 1557, the forest charter was issued, under which a special board was established to examine forest usage. In 1639, King Vladislaus IV issued the "Białowieża royal forest decree" (Ordynacja Puszczy J.K. Mości leśnictwa Białowieskiego). The document freed all serfs living in the forest in exchange for their service as osocznicy, or royal foresters. They were also freed of taxes in exchange for taking care of the forest. The forest was divided into 12 triangular areas (straże) with a centre in Białowieża.

Until the reign of King John II Casimir, the forest was mostly unpopulated. However, in the late 17th century, several small villages were established for development of local iron-ore deposits and tar production. The villages were populated with settlers from Masovia and Podlaskie and many of them still exist.

After the Partitions of Poland, Tsar Paul I turned all the foresters into serfs and handed them over to various Russian aristocrats and generals along with the parts of forest where they lived. Also, a large number of hunters were able to enter the forest, as all protection was abolished. Following this, the number of bison fell from more than 500 to fewer than 200 in 15 years. However, in 1801, Tsar Alexander I reintroduced the reserve and hired a small number of foresters to protect the animals, and by the 1830s there were 700 bison. However, most of the foresters (500 out of 502) took part in the November Uprising of 1830–31, and their posts were abolished, leading to a breakdown of protection.

Tsar Alexander II visited the forest in 1860 and decided to re-establish the protection of bison. Following his orders, locals killed all predators: wolves, bears and lynx. Between 1888 and 1917, the Russian tsars owned all of primaeval forest, which became the royal hunting reserve. The tsars sent bison as gifts to various European capitals, while at the same time populating the forest with deer, elk and other animals imported from around the empire.

The last Russian royalty visit was by Czar Nicholas II in 1912.

During World War I the forest suffered heavy losses. The German army seized the area in August 1915 and started to hunt the animals. During three years of German occupation, 200 kilometres (124 miles) of railway tracks were laid in the forest to support the local industry. Three lumber mills were built, in Hajnówka, Białowieża and Gródek. Up to 25 September 1915, at least 200 bison were killed, and an order was issued forbidding hunting in the reserve. However, German soldiers, poachers and Soviet marauders continued the slaughter until February 1919 when the area was captured by the Polish army. The last bison had been killed just a month earlier. Thousands of deer and wild boar had also been shot.

After the Polish–Soviet War in 1921, the core of the forest was declared a National Reserve. In 1923, Professor Józef Paczoski, a pioneer of the science of phytosociology, became a scientific manager of the forest reserves in the Białowieża Forest. He carried out detailed studies of the structure of forest vegetation there.

In 1923 it was known that only 54 European bison survived in zoos all around the world, none of them in Poland. In 1929, a small herd of four was bought by the Polish state from various zoos and from the Western Caucasus (where the bison was to become extinct just a few years later). These animals were of the slightly different Caucasian subspecies (Bison bonasus caucasicus). To protect them, in 1932 most of the forest was declared a national park. The reintroduction proved successful, and by 1939 there were 16 bison in Białowieża National Park. Two of them, from the zoo in Pszczyna, were descendants of a pair from the forest given to the Duke of Pszczyna by Tsar Alexander II in 1865.

In 1939 the local inhabitants of Polish ethnicity were deported to remote areas of the Soviet Union and replaced by Soviet forest workers. In 1941 the forest was occupied by Germans and the Russian Soviet inhabitants were also expelled. Hermann Göring planned to create the largest hunting reserve in the world there. After July 1941 the forest became a refuge for both Polish and Soviet partisans and Nazi authorities organised mass executions. A few graves of people who were killed by the Gestapo can still be seen in the forest. (Hermann Göring directed anti-partisan operations by Luftwaffe security battalions in the Białowieża Forest between 1942 and 1944 that resulted in the murder of thousands of Jews and Polish civilians.) In July 1944 the area was overtaken by the Red Army. Withdrawing Wehrmacht troops demolished the historic Białowieża hunting manor.

After the war, the forest's territory was divided between Poland and the Belarusian SSR of the Soviet Union. The chairman of the Polish Committee of National Liberation, Edward Ochab, wrote in his memoirs regarding the negotiations about the demarcation of the border in the area of Białowieża Forest. According to his view, the Soviet officials repeated many times that they were not interested in enlarging their vast state, but only in sorting out the issue of Belarusian and Ukrainian nationalities in the borderland area (Kresy). Ochab emphasized to his Soviet negotiators that the problem didn't exist in Białowieża Forest and that the forest had a special historical place in the Polish national memory as a place where guerilla fights took place during the uprising against the tsarist regime. In addition, Poland had its forests decimated by the Germans during the occupation of Poland and finally, the forest was Poland's raw material basin for the timber industry in Hajnówka. According to Ochab's memories, when Stalin fiercely insisted on the need to "close the case", Ochab requested a break for consultations in the nearby room. He told his associates from the PKWN that he would resign from his position as the chairman of that body, as he could not find enough spiritual strength and inner conviction to promote Polish–Soviet friendship. The conversation was interrupted and the delegation was escorted to the premises in the seat Union of Polish Patriots and waited for news from the Soviet government. After a half an hour or so, Soviet Foreign Minister Vyacheslav Molotov called and informed Ochab by phone that Stalin had agreed to transfer half of the forest to Poland including the village of Białowieża and congratulated him. According to Ochab, he was unhappy with the decision as he was counting on the entire Białowieża Forest.

The Soviet part was put under public administration while Poland reopened the Białowieża National Park in 1947. Belovezhskaya Pushcha was protected under Decision No. 657 of the Council of People's Commissars of the Soviet Union, 9 October 1944; Order No. 2252-P of the USSR Council of Ministers, 9 August 1957; and Decree No. 352 of the Byelorussian SSR Council of Ministers, 16 September 1991.

In December 1991, the Belavezha Accords, the decision to dissolve the Soviet Union, were signed at a meeting in the Belarusian part of the reserve by the leaders of Ukraine, Russia and Belarus.

The forest contains a number of large, ancient pedunculate oaks (Quercus robur), some of which are individually named. Trunk circumferences are measured at breast height, 130 cm (51 in) above the ground.

• Great Mamamuszi. Circumference 690 cm (270 in) (2005), height 34 m (112 ft). One of the thickest oaks in the forest, with a beautiful column-like trunk. The tree's name comes from Molière's The Bourgeois Gentleman, in which the main protagonist (Mr Jourdain) was appointed the Mamamouchi by a Turkish ambassador. Since 1989 the tree's circumference grew by 10 cm (3.9 in). Of all the oaks in Białowieża Forest with a circumference above 600 cm (240 in), it is in the best condition.
• The King of Nieznanowo. Circumference 620 cm (240 in), height 38 m (125 ft). This tree has one of the most columnar trunks among the oaks in Białowieża Forest. The first branches arise at the height of 18 m. It has been gradually dying since 1998. As of 2005, only two small branches still have leaves. Since the mid-1960s its trunk circumference has grown by about 45 cm (18 in).
• Emperor of the South. Circumference 610 centimetres (240 in), height 40 m (130 ft). The tree shows no clear signs of dying.
• Emperor of the North. Circumference 605 cm (238 in), height 37 m (121 ft). The tree has a very regular trunk and shows no clear signs of dying.
• Southern Cross. Circumference 630 cm (250 in), height 36 m (118 ft). At the base of the trunk it has a considerable lesion in the bark on the eastern side. From the mid-1960s its circumference has grown by 65 cm (26 in). The name comes from the shape of its crown, whose main branches evoke a cross.
• The Guardian of Zwierzyniec. Circumference 658 cm (259 in), height 37 m (121 ft). This is one of the thickest oaks in the forest. The tree is largely bent down westwards, which most probably has contributed to the large circumference of the trunk at its base. All the branches are live, indicating that the tree is in good condition.
• Barrel Oak. Circumference 740 cm (290 in), height over 30 m (98 ft). This tree is named for its barrel-shaped trunk, and is the oak which reaches the greatest trunk circumference among the Białowieża oaks. The tree is dead and largely devoid of bark, and is estimated to be around 450 years old.
• Dominator Oak. Circumference 680 cm (270 in), height over 36 m (118 ft). One of the thickest oaks of the Białowieża, the tree has been dead since 1992 and its trunk is now largely devoid of bark. For many years it dominated the Białowieża Forest as far as size is concerned. Its age is estimated at 450 years.
• The Jagiełło Oak. Circumference (when growing) 550 cm (220 in), height 39 m (128 ft). It blew down in 1974, but is probably the most famous of the trees in the forest. It is said that King Władysław II Jagiełło rested beneath it before the Battle of Grunwald (Bitwa Pod Grunwaldem) in 1410, although the tree is believed to have been only 450 years old when it blew down.
• Tsar Oak (Polish) (Polish: Dąb Car) of Poland. Circumference 640 cm (250 in), height 41 m (135 ft). The tree's volume has been estimated at 75 m (2,600 cu ft). It died in 1984, and for over 20 years it has been standing dead on the edge of the valley of Leśna Prawa river. Today the trunk is totally devoid of bark and some of the branches have broken off and lie at the base of the trunk.
• Patriarch Oak (Russian: Патриарх-Дуб). One of the oldest oaks in the Belarusian National Park, standing 31 m (102 ft) tall, having a diameter in excess of 2 m (6.6 ft), and being over 550 years of age. It stands 1 kilometre (0.6 miles) from the estate of Ded Moroz.

Some 84% of the 60,000 hectares (150,000 acres) of Polish forest is outside the national park; almost half of all the wood in the forest is dead – 10 times more than in managed forests – with half the 12,000 species depend on decaying logs, including the near-threatened beetle Cucujus cinnaberinus. Traditional forest management would remove the dead wood, as a fire risk. In 2011, Zdzisław Szkiruć, director of the Białowieża National Park, said that cutting and replanting allows for re-establishment of the forest in 50 years, rather than the 300–400 years that nature would require; environmentalist Janusz Korbel argued that the unique nature of the primeval forest demands a lighter style of management. Andrzej Kraszewski, Poland's Environment Minister from February 2010 to November 2011, sought to increase protection over the whole forest, starting with a more modest 12,000–14,000-hectare (30,000–35,000-acre) expansion, against opposition from the local community and the Forestry Service.

Environmentalists say that logging is threatening the flora and fauna in the forest, including species of rare birds, such as the white-backed woodpecker, who lost 30% of their population in forestry-managed areas in the 1990s and 2000s. Poland's state forestry board claims the logging is for protection and for ecological reasons, protecting against the European spruce bark beetle. In 2012, the amount of wood that can be extracted by foresters annually was briefly reduced from about 120,000 m (4,200,000 cu ft) to 48,500 m (1,700,000 cu ft), approximately 20,000,000 board feet, most which is sold locally, mainly as firewood.

On 25 March 2016, Jan Szyszko, Poland's Environment Minister, former forester and forestry academic, announced that he would approve a tripling of logging in the forest, from the 2012–21 limit of 63,000 m (2,200,000 cu ft) – almost exhausted at the time – to 188,000 m (6,600,000 cu ft), offering the excuse of "combatting an infestation of the bark beetle". Robert Cyglicki, head of Greenpeace Polska, argued that logging to fight the bark beetle would "bring more damage than benefits", gathering more than 120,000 signatures to petition Prime Minister Beata Szydło to reverse Szyszko's move. Greenpeace also said the logging could trigger the EU to launch punitive procedures against Poland for violating its Natura 2000 programme, though Szyszko claims that the logging plans would not apply to strictly protected areas, and claims that, rather than being 8,000 years old, as scientists claim, parts of the forest had been created by an "enterprising hand of man" on lands that centuries ago included fields of wheat and millet.

Large-scale logging started in 2017. 190,000 cubic metres of wood (160,000 to 180,000 trees) was felled, the largest volume of logging since 1988. The Polish government has ignored pleas from UNESCO to stop logging the old-growth parts of the forest, as well as a court order of the European Court of Justice to halt the logging activities. The final verdict fell on 17 April 2018, ruling that EU law has been infringed.

• The forest is the subject of a Belarusian ballad Belovezhskaya Pushcha, composed in 1975 by Aleksandra Pakhmutova, with lyrics by Nikolai Dobronravov, performed by Belarusian folk band Pesniary.
• Białowieża Forest is mentioned throughout Alan Weisman's book The World Without Us (2007), which investigates places that have been abandoned or left alone and imagines what they would be like if Earth's human population suddenly disappeared.
• British historian Simon Schama devotes several chapters of his book Landscape and Memory (1995) to the Białowieża Forest.
• In late 2017, Wojtek Voiteque Kowalik, a senior copy editor at the Polish advertising firm Ogilvy, decided to work with Greenpeace Poland to spread awareness of the Białowieża Forest and the logging threatening it. Kowalik decided to use the game Minecraft, as he wanted to capitalize on its playerbase of 87 million. Kowalik reasoned Minecraft was a form of social media, drawing parallels between the YouTube and Twitch communities dedicated to the game and the video arcades of his youth. Kowalik contacted Danish company GeoBoxers, who had previously recreated all of Denmark in Minecraft in 1:1 scale, and convinced them to do the same for Białowieża Forest. In return Ogilvy and Greenpeace provided reference material for Geoboxers in the form of a 3D topographical map of the 700-square-kilometre (270 sq mi) forest made from hundreds of images and maps of Białowieża Forest that took six weeks to complete.
• The action of a role-playing video game Werewolf: The Apocalypse – Heart of the Forest developed by Different Tales and released on 13 October 2020 (for MS Windows, Linux and Mac OS) takes place in Białowieża Forest. The player takes the role of Maia Boroditch, an American woman of Polish descent, who has recurring nightmares about a forest and wolves, and travels to Białowieża in Poland to learn about her family history and discovers secrets of the primeval Białowieża Forest.
• The forest is mentioned in Upton Sinclair's seminal novel The Jungle (1906). It is the birthplace of protagonist Jurgis Rudkus.
• The forest is a key focus in the 2021 nonfiction book Into the Forest: A Holocaust Story of Survival, Triumph, and Love by Rebecca Frankel. The book describes the experience of a Jewish family that fled into the forest during the Nazi occupation in 1942.
• The forest is the setting of author-translator Jennifer Croft's 2024 novel The Extinction of Irena Rey.

• Tourism in Poland
• List of national parks of Belarus
• List of national parks of Poland
• List of old-growth forests
• Perućica, a primeval forest in Europe (Bosnia and Herzegovina)
• Virgin Komi Forests, the largest forest in Europe
• Western Caucasus, the largest bison (wisent) habitat
• Hercynian Forest, an ancient forest that stretched across Western Central Europe, mentioned by Julius Caesar in De Bello Gallico

• The UNESCO official site
• Białowieża National Park
• Oaks from Bialowieza (archived 6 May 2008)
• Trees of Białowieża National Park
• BBC radio documentary about the forest (2002)