Iran, also known as Persia officially the Islamic Republic of Iran, is a country in Western Asia. It is bordered to the northwest by Armenia and Azerbaijan; with Kazakhstan and Russia across the Caspian Sea; to the northeast by Turkmenistan; to the east by Afghanistan and Pakistan; to the south by the Persian Gulf and the Gulf of Oman; and to the west by Turkey and Iraq. Comprising a land area of 1,648,195 km2 (636,372 sq mi), it is the second-largest nation in the Middle East and the 18th-largest in the world; with 78.4 million inhabitants,
Iran is home to one of the world's oldest civilizations, beginning with the formation of the Proto-Elamite and Elamite kingdom in 3200–2800 BC. The Iranian Medes unified the area into the first of many empires in 625 BC, after which it became the dominant cultural and political power in the region. Iran reached the pinnacle of its power during the Achaemenid Empire founded by Cyrus the Great in 550 BC, which at its greatest extent comprised major portions of the ancient world, stretching from parts of the Balkans (Thrace, Paeonia and Macedonia) in the west, to the Indus Valley in the east, making it the largest empire the world had yet seen.
Iran is a founding member of the UN, ECO, NAM, OIC and OPEC. Its unique political system, based on the 1979 constitution, combines elements of a parliamentary democracy with a religious theocracy governed by the country's clergy, wherein the Supreme Leader wields significant influence. A multicultural nation comprising numerous ethnic and linguistic groups, most inhabitants are Shi'ites, the Iranian rial is the currency, and Persian is the official language.