Estonia (Estonian: Eesti [esti] (listen)), officially the Republic of Estonia (Estonian: Eesti Vabariik), is a country in Northern Europe. It is bordered to the north by the Gulf of Finland across from Finland, to the west by the Baltic Sea across from Sweden, to the south by Latvia, and to the east by Lake Peipus and Russia. The territory of Estonia consists of the mainland, the larger islands of Saaremaa and Hiiumaa, and over 2,200 other islands and islets on the eastern coast of the Baltic Sea, covering a total area of 45,339 square kilometres (17,505 sq mi). The capital city Tallinn and Tartu are the two largest urban areas of the country. The Estonian language is the autochthonous and the official language of Estonia; it is the first language of the majority of its population, as well as the world's second most spoken Finnic language.

The land of what is now modern Estonia has been inhabited by Homo sapiens since at least 9,000 BC. The medieval indigenous population of Estonia was one of the last "pagan" civilisations in Europe to adopt Christianity following the Papal-sanctioned Livonian Crusade in the 13th century. After centuries of successive rule by the Teutonic Order, Denmark, Sweden, and the Russian Empire, a distinct Estonian national identity began to emerge in the mid-19th century. This culminated in the 24 February 1918 Estonian Declaration of Independence from the then warring Russian and German Empires. After the end of World War I, in the 19181920 War of Independence, Estonians were able to repel the Bolshevik Russian invasion and successfully defended their newborn freedom. Democratic throughout most of the interwar period, Estonia declared neutrality at the outbreak of World War II, but the country was repeatedly contested, invaded and occupied, first by Stalinist Soviet Union in 1940, then by Nazi Germany in 1941, and ultimately reoccupied in 1944 by, and annexed into, the USSR as an administrative subunit (Estonian SSR). After the loss of its de facto independence to the Soviet Union, Estonia's de jure state continuity was preserved by diplomatic representatives and the government-in-exile. Following the bloodless Estonian "Singing Revolution" of 19881990, the nation's de facto independence was restored on 20 August 1991.

Estonia is a developed country, with a high-income advanced economy, ranking very highly in the Human Development Index. The sovereign state of Estonia is a democratic Unitary parliamentary republic, administratively subdivided into 15 maakond (counties). With a population of just over 1.3 million, it is one of the least populous members of the European Union, the Eurozone, the OECD, the Schengen Area, and NATO. Estonia has consistently ranked highly in international rankings for quality of life, education, press freedom, digitalisation of public services and the prevalence of technology companies.

The largest expansion of the European Union (EU), in terms of territory, number of states, and population took place on 1 May 2004.

The simultaneous accessions concerned the following countries (sometimes referred to as the "A10" countries): Cyprus, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia and Slovenia. Seven of these were part of the former Eastern Bloc (of which three were from the former Soviet Union and four were and still are members of the Central European alliance Visegrád Group). Slovenia was a non-aligned country prior to the independence, and it was one of the former republics of Yugoslavia (together sometimes referred to as the "A8" countries), and the remaining two were Mediterranean islands and two Members of Commonwealth of Nations.

Part of the same wave of enlargement was the accession of Bulgaria and Romania in 2007, who were unable to join in 2004, but, according to the Commission, constitute part of the fifth enlargement.