Lithuania, officially the Republic of Lithuania, is a country in the Baltic region of Europe. It is one of three Baltic states and lies on the eastern shore of the Baltic Sea, bordered by Latvia to the north, Belarus to the east and south, Poland to the south, and the Russian semi-exclave of Kaliningrad Oblast to the southwest, with a maritime border with Sweden to the west. Lithuania covers an area of 65,300 km² (25,200 sq mi), with a population of 2.9 million. Its capital and largest city is Vilnius; other major cities include Kaunas, Klaipėda, Šiauliai and Panevėžys. Lithuanians are the titular nation, belong to the ethnolinguistic group of Balts, and speak Lithuanian.

For millennia, the southeastern shores of the Baltic Sea were inhabited by various Baltic tribes. In the 1230s, Lithuanian lands were united for the first time by Mindaugas, who formed the Kingdom of Lithuania on 6 July 1253. Subsequent expansion and consolidation resulted in the Grand Duchy of Lithuania, which by the 14th century was the largest country in Europe. In 1386, the grand duchy entered into a de facto personal union with the Crown of the Kingdom of Poland. The two realms were united into the Polish-Lithuanian Commonwealth in 1569, forming one of the largest and most prosperous states in Europe. The commonwealth lasted more than two centuries, until neighbouring countries gradually dismantled it between 1772 and 1795, with the Russian Empire annexing most of Lithuania's territory.

Towards the end of World War I, Lithuania declared independence in 1918, founding the modern Republic of Lithuania. In World War II, Lithuania was occupied by the Soviet Union, then by Nazi Germany, before being reoccupied by the Soviets in 1944. Lithuanian armed resistance to the Soviet occupation lasted until the early 1950s. On 11 March 1990, a year before the formal dissolution of the Soviet Union, Lithuania became the first Soviet republic to break away when it proclaimed the restoration of its independence.

Lithuania is a developed country with a high-income and an advanced economy ranking very high in Human Development Index. Lithuania ranks highly in digital infrastructure, press freedom and happiness. It is a member of the United Nations, the European Union, the Council of Europe, the Council of the Baltic Sea States, the Eurozone, the Nordic Investment Bank, the International Monetary Fund, the Schengen Agreement, NATO, OECD and the World Trade Organization. It also participates in the Nordic-Baltic Eight (NB8) regional co-operation format.

The spelling of Lithuania was a later addition to the original Latinate Lituania since 1800 as a form of hyperforeignism influenced by Greek loanwords with the theta; it is ultimately from Lithuanian: Lietuva. The first known record of Lietuva is in a 1009 story of Saint Bruno in the Annals of Quedlinburg. The chronicle records Latinized form of the name Lietuva: Litua. The true meaning of the name is unknown, and scholars still debate it. There are a few plausible versions.

Lietava, a small stream near Kernavė—the core area of the early Lithuanian state and a possible first capital of the eventual Grand Duchy of Lithuania—is usually credited as the source of the name. However, the stream is very small, and some find it improbable that such a small and localized body of water could have lent its name to an entire nation. On the other hand, such naming is not unprecedented in world history.

Artūras Dubonis proposed another hypothesis, that Lietuva relates to the word leičiai (plural of leitis). From the middle of the 13th century, leičiai were a distinct warrior social group of the Lithuanian society subordinate to the Lithuanian ruler or the state itself. The word leičiai is used in 14–16th century historical sources as an ethnonym for Lithuanians (but not Samogitians) and is still used, usually poetically or in historical contexts, in the Latvian language, which is closely related to Lithuanian.

The history of Lithuania dates back to settlements founded about 10,000 years ago. The first people settled in the territory of Lithuania after the Last Glacial Period in the 10th millennium BC: Kunda, Neman and Narva cultures. They were traveling hunters. In the 8th millennium BC the climate became warmer and forests developed. The inhabitants of what is now Lithuania travelled less and engaged in local hunting, gathering and fresh-water fishing. The Indo-Europeans, who arrived in the 3rd – 2nd millennium BC, mixed with the local population and formed various Baltic tribes. The Balts did not maintain close cultural or political contacts with the Roman Empire, while maintaining trade contacts via the Amber Road.