Western Asia or Southwestern Asia is the westernmost subregion of Asia. It includes Anatolia, the Arabian Peninsula, Iran, the Levant, Mesopotamia, the Sinai Peninsula, and Transcaucasia. The region is considered to be separated from Africa by the Isthmus of Suez, and separated from Europe by the waterways of the Turkish Straits and the drainage divide of the Caucasus Mountains. Central Asia lies to the northeast of Western Asia while South Asia lies to the east.
20 countries are located fully or partly in Western Asia, out of which 13 are part of the Arab States. The most populous countries in Western Asia are Turkey (partly in Southeast Europe), Iran, Iraq, Saudi Arabia, and Yemen. The total population of Western Asia is estimated to be 300 million (as of 2015).
Western Asia is primarily arid and semi-arid, and can be subject to drought, but it also contains vast expanses of forest and fertile valleys. The region consists of grasslands, rangelands, deserts, and mountains. Water shortages are a problem in many parts of West Asia, with rapidly growing populations increasing demands for water, while salinization and pollution threaten water supplies. Major rivers, including the Tigris and Euphrates, provide sources for irrigation water to support agriculture.