Bahrain, officially the Kingdom of Bahrain, is an island country in West Asia. Situated on the Persian Gulf, it comprises a small archipelago of 50 natural islands and an additional 33 artificial islands, centred on Bahrain Island, which makes up around 83 percent of the country's landmass. Bahrain is situated between Qatar and the northeastern coast of Saudi Arabia, to which it is connected by the King Fahd Causeway. The population is 1,588,670 as of 2024, of whom 739,736 (46.6% of the population) are Bahraini nationals, and 848,934 are expatriates (53.4% of the population). Bahrain spans some 760 square kilometres (290 sq mi) and is the third-smallest nation in Asia after Maldives and Singapore. The capital and largest city is Manama.

The area that straddles the present-day territory of Bahrain was once the site of the ancient Dilmun civilisation. It has been famed since antiquity for its pearl fisheries, which were considered the best in the world into the 19th century. Bahrain was one of the earliest areas to be influenced by Islam, during the lifetime of Muhammad in 628. Following a period of Arab rule, Bahrain was ruled by the Portuguese Empire from 1521 until 1602, when they were expelled by Shah Abbas the Great of the Safavid Iran. In 1783, the Bani Utbah and allied tribes captured Bahrain from Nasr Al-Madhkur. It has since been ruled by the Al Khalifa royal family, with Ahmed al Fateh as Bahrain's first hakim. In the late 19th century, following successive treaties with the British, Bahrain became a protectorate of the United Kingdom. In 1971, it declared independence. Formerly an emirate, Bahrain was declared a semi-constitutional monarchy in 2002, and Article 2 of the constitution made sharia a principal source for legislation. In 2011, the country experienced protests inspired by the regional Arab Spring. The ruling Sunni Muslim Al Khalifa royal family has been criticised for violating the human rights of groups including dissidents, political opposition figures, and its Shia Muslim population.

Bahrain is known as one of the first post-oil economies in the Persian Gulf, the result of decades of investing in the banking and tourism sectors; many of the world's largest financial institutions have a presence in Manama. Oil revenues still constitute a significant part of its government budget. It is recognised by the World Bank as a high-income economy. Bahrain is a member of the United Nations, the Non-Aligned Movement, the Arab League, the Organisation of Islamic Cooperation, and the Gulf Cooperation Council. It is a Dialogue partner of the Shanghai Cooperation Organization.

Bahrain is the dual form of the Arabic word Bahr (meaning literally "sea"), so al-Bahrayn originally means literally "the two seas". However, the name has been lexicalised as a feminine proper noun and does not follow the grammatical rules for duals; thus its form is always Bahrayn and never Bahrān, the expected nominative form. Endings are added to the word with no changes, as in the name of the national anthem Bahraynunā ("our Bahrain") or the demonym Bahraynī. The medieval grammarian al-Jawahari commented on this, saying that the more formally correct term Bahrī (lit. 'belonging to the sea') would have been misunderstood and so was unused.

It remains disputed which "two seas" the name Bahrayn originally refers to. The term appears five times in the Quran but does not refer to the modern island—originally known to the Arabs as Awal. Today, Bahrain's "two seas" are generally taken to be the bay east and west of the island, the seas north and south of the island, or the salt and fresh water present above and below the ground. In addition to wells, there are areas of the sea north of Bahrain where fresh water bubbles up in the middle of the saltwater as noted by visitors since antiquity. An alternative theory concerning Bahrain's toponymy is offered by the al-Ahsa region, which suggests that the two seas were the "Great Green Ocean" (the Persian Gulf) and Al-Asfar Lake on the Arabian mainland.^{[citation needed]}

Until the late Middle Ages, "Bahrain" referred to the region of Eastern Arabia that included southern Iraq, Kuwait, Al-Hasa, Qatif, and Bahrain. The region stretched from Basra in Iraq to the Strait of Hormuz in Oman. This was Iqlīm al-Bahrayn's "Bahrayn Province". When the term "Bahrain" began to refer solely to the Awal archipelago is unknown. The entire coastal strip of Eastern Arabia was known as "Bahrain" for a millennium. The island and kingdom were also commonly spelled Bahrein.

Bahrain was home to Dilmun, an important Bronze Age trade centre linking Mesopotamia and the Indus Valley. Bahrain was later ruled by the Sumerians and Babylonians. From the 6th to 3rd century BC, Bahrain was part of the Achaemenid Empire. By about 250 BC, Parthia brought the Persian Gulf under its control and extended its influence as far as Oman. The Parthians established garrisons along the southern coast of the Persian Gulf to control trade routes.

During the classical era, Bahrain was referred to by the ancient Greeks as Tylos, the centre of pearl trading, when the Greek admiral Nearchus serving under Alexander landed on Bahrain. Nearchus is believed to have been the first of Alexander's commanders to visit the island, and he found a verdant land that was part of a wide trading network; he recorded: "That on the island of Tylos, situated in the Persian Gulf, are large plantations of cotton trees, from which are manufactured clothes called sindones, of strongly differing degrees of value, some being costly, others less expensive. The use of these is not confined to India, but extends to Arabia." The Greek historian Theophrastus states that much of Bahrain was covered by these cotton trees and that Bahrain was famous for exporting walking canes engraved with emblems that were customarily carried in Babylon. Alexander had planned to settle Greek colonists in Bahrain, and although it is not clear that this happened on the scale he envisaged, Bahrain became very much part of the Hellenised world: the language of the upper classes was Greek (although Aramaic was in everyday use). Local coinage shows a seated Zeus, who may have been worshipped there as a syncretised form of the Arabian sun-god Shams. Tylos was also the site of Greek athletic contests.