Asia is the largest and most populous of the Earth's continents. It is traditionally defined as part of the landmass of Africa-Eurasia lying east of the Suez Canal, east of the Ural Mountains, and southeast of the Caucasus Mountains and the Caspian and Black Seas. About 60% of the world's human population lives in Asia, of whom only 2% live in the northern and interior half (Siberia, Mongolia, Kazakhstan, Xinjiang, Tibet, Qinghai, western Uzbekistan and Turkmenistan); the other 98% live in the remaining half.

Continents are concepts of human geography (i.e., landscapes and landforms as interpreted by humans), not of geology or physical geography, and definitions may vary. The concept of the three continents of the Old World goes back to classical antiquity with the etymology of the word also having roots in the ancient Near and Middle East. The demarcation between Asia and Africa is the Isthmus of Suez and the Red Sea. The boundary between Asia and Europe is commonly believed to run via the Dardanelles, the Sea of Marmara, the Bosporus, through the Black Sea, the Caucasus Mountains, the Caspian Sea, the Ural River to its source, and the Ural Mountains to the Kara Sea near Kara, Russia.

It is sometimes unclear what Asia precisely consists of. In some definitions, it may exclude Turkey, the Middle East and/or Russia. Asia is sometimes used more strictly in reference to Asia Pacific, which does not include the Middle East or Russia, and does include islands in the Pacific Ocean — a number of which may also be considered part of Australasia and/or Oceania. Asia contains the Indian subcontinent, Arabian subcontinent, and a piece of the North American plate in Siberia.

Central Asia

There is no absolute consensus in the usage of this term. Usually, Central Asia includes:

the Central Asian Republics of Kazakhstan (excluding its small European territory), Uzbekistan, Tajikistan, Turkmenistan and Kyrgyzstan. Afghanistan, Mongolia, and the western regions of China are also sometimes included. Former Soviet states in the Caucasus region.

Central Asia is currently geopolitically important because international disputes and conflicts over oil pipelines, Nagorno-Karabakh, and Chechnya, as well as the presence of U.S. military forces in Afghanistan.

East Asia (or Far East)

This area includes:

The Pacific Ocean island countries of Taiwan and Japan.

Further information: Political status of Taiwan

North and South Korea on the Korean Peninsula. China, but sometimes only the eastern regions

Sometimes the nations of Mongolia and Vietnam are also included in East Asia.

More informally, Southeast Asia is included in East Asia on some occasions.

North Asia

This term is rarely used by geographers, but usually it refers to the bigger Asian part of Russia, also known as Siberia. Sometimes the northern parts of other Asian nations, such as Kazakhstan are also included in Northern Asia.

South Asia (or Indian Subcontinent)

South Asia is also referred to as the Indian Subcontinent. It includes:

the Himalayan States of India, Pakistan, Nepal, Bhutan and Bangladesh. the Indian Ocean nations of Sri Lanka and the Maldives. India's Andaman, Nicobar and Lakshadweep islands also lie in the Indian Ocean. the peninsular India (also known as the Deccan Plateau) sometimes Afghanistan is also included into this category.

Southeast Asia

This region contains the Malay Peninsula, Indochina and islands in the Indian Ocean and Pacific Ocean. The countries it contains are:

In mainland Southeast Asia, the countries Myanmar, Thailand, Laos, Cambodia and Vietnam. In Maritime Southeast Asia, the countries of Malaysia, Brunei, the Philippines, Singapore and Indonesia (some of the Indonesian islands also lie in the Melanesia region of Oceania). East Timor (also Melanesian) is sometimes included too.

The country of Malaysia is divided in two by the South China Sea, and thus has both a mainland and island part.

Southwest Asia (or Middle East, Near East or West Asia)

This can also be called by the Western term Middle East, which is commonly used by Europeans and Americans. Middle East (to some interpretations) is often used to also refer to some countries in North Africa. Southwest Asia can be further divided into:

Anatolia (i.e. Asia Minor), constituting the Asian part of Turkey. The island nation of Cyprus in the Mediterranean Sea. The Levant or Near East, which includes Syria, Israel, Jordan, Lebanon, Iraq and the Asian portion of Egypt. The Arabian peninsula, including Saudi Arabia, United Arab Emirates, Bahrain, Qatar, Oman, Yemen and Kuwait. The Caucasus region (which straddles both Asia and Europe), namely Transcaucasia, including a small portion of Russia and, arguably, most if not all of Georgia, Armenia, and Azerbaijan. The Iranian Plateau, containing Iran and parts of other neighbouring nations.

The history of Asia can be seen as the distinct histories of several peripheral coastal regions, East Asia, South Asia, and the Middle East, linked by the interior mass of the Central Asian steppe.

The coastal periphery was home to some of the world's earliest known civilizations, with each of the three regions developing early civilizations around fertile river valleys. The civilizations in Mesopotamia, the Indus Valley, and the Yangtze shared many similarities and likely exchanged technologies and ideas such as mathematics and the wheel. Other notions such as that of writing likely developed individually in each area. Cities, states and empires developed in these lowlands.

The steppe region had long been inhabited by mounted nomads, and from the central steppes they could reach all areas of Asia. The earliest known such central expansion out of the steppe is that of the Indo-Europeans, who spread their languages into the Middle East, India, and in the Tocharians to the borders of China. The northern part of Asia, covering much of Siberia, was inaccessible to the steppe nomads, due to the dense forests and the tundra. These areas were very sparsely populated.

The centre and periphery were kept separate by mountains and deserts. The Caucasus, Himalaya, Karakum Desert and Gobi Desert formed barriers that the steppe horsemen could only cross with difficulty. While technologically and culturally, the urban city dwellers were more advanced, they could do little militarily to defend against the mounted hordes of the steppe. However, the lowlands did not have enough open grasslands to support a large horsebound force. Thus the nomads who conquered states in China, India, and the Middle East were soon forced to adapt to the local societies.