Asia, largest of the Earth’s seven continents, lying almost entirely in the Northern Hemisphere. With outlying islands, it covers an estimated 44,391,000 sq km (17,139,000 sq mi), or about 30 percent of the world’s total land area. Its peoples account for three-fifths of the world’s population; in 2005 Asia had an estimated 3.91 billion inhabitants.

Most geographers regard Asia as bounded on the north by the Arctic Ocean, on the east by the Bering Strait and the Pacific Ocean, on the south by the Indian Ocean, and on the southwest by the Red Sea and Mediterranean Sea. On the west, the conventional boundary between Europe and Asia is drawn at the Ural Mountains, continuing south along the Ural River to the Caspian Sea, then west along the Caucasus Mountains to the Black Sea. Some geographers include Europe and Asia together in a larger Eurasian region, noting that western Asian countries, such as Turkey, merge almost imperceptibly into Europe.

The continental mainland stretches from the southern end of the Malay Peninsula to Cape Chelyuskin in Siberia. Its westernmost point is Cape Baba in northwestern Turkey, and its easternmost point is Cape Dezhnyov in northeastern Siberia. The continent’s greatest width from east to west is 8,500 km (5,300 mi). The lowest and highest points on the Earth’s surface are in Asia, namely, the shore of the Dead Sea (408 m/1,340 ft below sea level in 1996) and Mount Everest (8,850 m/29,035 ft above sea level).

South of the mainland in the Indian Ocean are Sri Lanka and smaller island groups, such as the Maldives and the Andaman and Nicobar islands. To the southeast is an array of archipelagoes and islands that extend east to the Oceanic and Australian realms. Among these islands are those of Indonesia, including Java, Sumatra, Sulawesi, and Borneo. The western end of the island of New Guinea is within Indonesia and for that reason geographers occasionally consider it part of Asia. In this encyclopedia, however, it is treated as a part of the Pacific Islands. The Philippine Islands, which include Luzon and Mindanao, are also among the Southeast Asian islands. To their north lie Taiwan, the Chinese island of Hainan, the islands of Japan, and the Russian island of Sakhalin.

Because of its vast size and diverse character, Asia is divided into five major realms: East Asia, including China, Mongolia, North Korea, South Korea, and Japan; Southeast Asia, including Myanmar (formerly known as Burma), Thailand, Cambodia, Laos, Vietnam, Malaysia, Singapore, Indonesia, Brunei, and the Philippines; South Asia, including India, Bangladesh, Pakistan, Sri Lanka, Maldives, Nepal, and Bhutan; and Southwest Asia, including Afghanistan, Iran, Iraq, Turkey, Cyprus, Armenia, Azerbaijan, Georgia, Syria, Lebanon, Israel, Jordan, Saudi Arabia, Yemen, Oman, United Arab Emirates, Qatar, Bahrain, and Kuwait. Most of the countries of Southwest Asia are also considered part of the Middle East, a loosely defined region that includes Egypt. Afghanistan and Myanmar are sometimes considered part of South Asia, but most geographers place Afghanistan in Southwest Asia and Myanmar in Southeast Asia. The fifth realm consists of the area of Russia that lies east of the Ural Mountains (Russian Asia) and the states of Central Asia that were formerly part of the Union of Soviet Socialist Republics (USSR). These states are Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, Uzbekistan.

The continent may also be divided into two broad cultural realms: that which is predominantly Asian in culture (East Asia, Southeast Asia, and South Asia) and that which is not (Southwest Asia, Central Asia, and Russian Asia). There is enormous cultural diversity within both regions, however.