Eurasia () is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago in the east. The continental landmass is bordered by the Atlantic Ocean and Africa to the west, the Pacific Ocean to the east, the Arctic Ocean to the north, and by Africa, the Mediterranean Sea, and the Indian Ocean to the south. The division between Europe and Asia as two continents is a historical social construct, as much of their borders is over land; thus, in some parts of the world, Eurasia is recognized as the largest of the six, five, or four continents on Earth. In geology, Eurasia is often considered as a single rigid megablock. However, the rigidity of Eurasia is debated based on paleomagnetic data.
Eurasia covers around 55,000,000 square kilometres (21,000,000 sq mi), or around 36.2% of the Earth's total land area; and is home to the largest country in the world, Russia. The landmass contains well over 5 billion people, equating to approximately 70% of the human population. Humans first settled in Eurasia between 60,000 and 125,000 years ago. Some major islands, including Great Britain, Iceland, Ireland, and Sri Lanka, as well as those of Japan, the Philippines, and most of Indonesia, are often included in the popular definition of Eurasia, despite being separate from the contiguous landmass.
According to some geographers physiographically, Eurasia is a single continent. The concepts of Europe and Asia as distinct continents date back to antiquity, and their borders are geologically arbitrary and have historically been subjected to occasional change. Eurasia is connected to Africa at the Suez Canal, and Eurasia is sometimes combined with Africa to make the largest contiguous landmass on Earth called Afro-Eurasia. Due to the vast landmass and differences in latitude, Eurasia exhibits all types of climate under the Köppen classification, including the harshest types of hot and cold temperatures, high and low precipitation and various types of ecosystems.
Eurasia formed between 375 and 325 million years ago with the merging of Siberia, Kazakhstania, and Baltica, which was joined to Laurentia, now North America, to form Euramerica. Chinese cratons collided with Siberia's southern coast.
Eurasia has been the host of many ancient civilizations, including those based in Mesopotamia, the Indus Valley and China. In the Axial Age (mid-first millennium BC), a continuous belt of civilizations stretched through the Eurasian subtropical zone from the Atlantic to the Pacific. This belt became the mainstream of world history for two millennia.
Originally, “Eurasia” is a geographical notion: in this sense, it is simply the biggest continent; the combined landmass of Europe and Asia. However, geopolitically, the word has several meanings, reflecting specific geopolitical interests. “Eurasia” is one of the most important geopolitical concepts and it figures prominently in the commentaries on the ideas of Halford Mackinder. As Zbigniew Brzezinski observed on Eurasia:
“... how America "manages" Eurasia is critical. A power that dominates “Eurasia” would control two of the world’s three most advanced and economically productive regions. A mere glance at the map also suggests that control over “Eurasia” would almost automatically entail Africa’s subordination, rendering the Western Hemisphere and Oceania geopolitically peripheral to the world’s central continent. About 75 per cent of the world’s people live in “Eurasia”, and most of the world’s physical wealth is there as well, both in its enterprises and underneath its soil. “Eurasia” accounts for about three-fourths of the world’s known energy resources.”
The Russian "Eurasianism" corresponded initially more or less to the land area of Imperial Russia in 1914, including parts of Eastern Europe. One of Russia's main geopolitical interests lies in ever closer integration with those countries that it considers part of “Eurasia.” This concept is further integrated with communist eschatology by author Alexander Dugin as the guiding principle of "self-sufficiency of a large space" during expansion.
The term Eurasia gained geopolitical reputation as one of the three superstates in 1984, George Orwell's novel where constant surveillance and propaganda are strategic elements (introduced as reflexive antagonists) of the heterogeneous dispositif such metapolitical constructs use to control and exercise power.
Across Eurasia, several single markets have emerged including the Eurasian Economic Space, European Single Market, ASEAN Economic Community and the Gulf Cooperation Council. There are also several international organizations and initiatives which seek to promote integration throughout Eurasia, including:
In ancient times, the Greeks classified Europe (derived from the mythological Phoenician princess Europa) and Asia which to the Greeks originally included Africa  (derived from Asia, a woman in Greek mythology) as separate "lands". Where to draw the dividing line between the two regions is still a matter of discussion. Especially whether the Kuma-Manych Depression or the Caucasus Mountains form the southeast boundary is disputed, since Mount Elbrus would be part of Europe in the latter case, making it (and not Mont Blanc) Europe's highest mountain. Most accepted is probably the boundary as defined by Philip Johan von Strahlenberg in the 18th century. He defined the dividing line along the Aegean Sea, Dardanelles, Sea of Marmara, Bosporus, Black Sea, Kuma–Manych Depression, Caspian Sea, Ural River, and the Ural Mountains. However, at least part of this definition has been subject to criticism by many modern analytical geographers like Halford Mackinder, who saw little validity in the Ural Mountains as a boundary between continents.
In modern usage, the term "Eurasian" is a demonym usually meaning "of or relating to Eurasia" or "a native or inhabitant of Eurasia". It is also used to describe people of combined "Asian" and "European" descent.
Located primarily in the eastern and northern hemispheres, Eurasia is considered a supercontinent, part of the supercontinent of Afro-Eurasia or simply a continent in its own right. In plate tectonics, the Eurasian Plate includes Europe and most of Asia but not the Indian subcontinent, the Arabian Peninsula or the area of the Russian Far East east of the Chersky Range.
From the point of view of history and culture, Eurasia can be loosely subdivided into Western and Eastern Eurasia.
Nineteenth-century Russian philosopher Nikolai Danilevsky defined Eurasia as an entity separate from Europe and Asia, bounded by the Himalayas, the Caucasus, the Alps, the Arctic, the Pacific, the Atlantic, the Mediterranean, the Black Sea and the Caspian Sea, a definition that has been influential in Russia and other parts of the former Soviet Union. Nowadays, partly inspired by this usage, the term Eurasia is sometimes used to refer to the post-Soviet space – in particular Russia, the Central Asian republics, and the Transcaucasus republics – and sometimes also adjacent regions such as Turkey and Mongolia.
The word "Eurasia" is often used in Kazakhstan to describe its location. Numerous Kazakh institutions have the term in their names, like the L. N. Gumilev Eurasian National University (Kazakh: Л. Н. Гумилёв атындағы Еуразия Ұлттық университеті; Russian: ) (Lev Gumilev's Eurasianism ideas having been popularized in Kazakhstan by Olzhas Suleimenov), the Eurasian Media Forum, the Eurasian Cultural Foundation (Russian: Евразийский фонд культуры), the Eurasian Development Bank (Russian: Евразийский банк развития), and the Eurasian Bank. In 2007 Kazakhstan's president, Nursultan Nazarbayev, proposed building a "Eurasia Canal" to connect the Caspian Sea and the Black Sea via Russia's Kuma-Manych Depression to provide Kazakhstan and other Caspian-basin countries with a more efficient path to the ocean than the existing Volga-Don Canal.
This usage can also be seen in the names of Eurasianet, The Journal of Eurasian Studies, and the , as well as the titles of numerous academic programmes at US universities.