Eurasia (/jʊəˈreɪʒə/ yoor-AY-zhə, also UK: /-ʃə/ -⁠shə) is the largest continental area on Earth, comprising all of Europe and Asia. According to some models of the world, physio-graphically, Eurasia is a single continent. The concept of Europe and Asia as distinct continents dates back to antiquity, but their borders have historically been subject to change. For example, the ancient Greeks originally included Africa in Asia but classified Europe as separate land. Eurasia is connected to Africa at the Suez Canal, and the two are sometimes combined to describe the largest contiguous landmass on Earth, Afro-Eurasia.

Eurasia has been the host of many ancient civilizations, including those based in Mesopotamia, Egypt, the Indus Valley and China. In the Axial Age (mid-first millennium BCE), 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.

New connections emerged between the subregions of Eurasia from the Age of Discovery onwards, with the Iberians discovering new maritime routes in the 1490s, and the 1869 completion of the Suez Canal having paved the way for direct passage through the Indo-Mediterranean and the wave of Western European "New Imperialism" that dominated Africa and Asia until the mid-20th century. The communist presence in Eurasia (primarily driven by the Soviet Union) then dominated much of the continent until the end of the Cold War in 1991.

Primarily in the Northern and Eastern Hemispheres, Eurasia spans from Iceland and the Iberian Peninsula in the west to the Russian Far East, and from the Russian Far North to Maritime Southeast Asia in the south, but other specific geographical limits of Eurasia states that the southern limit is in the Weber's line. Eurasia is bordered by Africa to the southwest, the Atlantic Ocean to the west, the Arctic Ocean to the north, the Pacific Ocean to the east, and the Indo-Mediterranean to the south. The division between Europe and Asia as two continents is a historical social construct, as neither fits the usual definition; thus, in some parts of the world, Eurasia is recognized as the largest of the six, five, or four continents on Earth.

Eurasia covers around 55 million square kilometres (21 million square miles), or around 36.2% of the Earth's total land area. The landmass contains well over 5 billion people, equating to approximately 70% of the human population. Humans first settled in Eurasia from Africa 125,000 years ago.

The coastline of Eurasia [uk] contains many peninsulas, including the Arabian Peninsula, Korean Peninsula, Indian subcontinent, Anatolia Peninsula, Kamchatka Peninsula, and the Italian Peninsula.

Due to its vast size and differences in latitude, Eurasia exhibits all types of climates under the Köppen classification, including the harshest types of hot and cold temperatures, high and low precipitation, and various types of ecosystems.

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.