Location of Bulgaria (dark green) Bulgaria , officially the Republic of Bulgaria , is a country in Southeast Europe . Located west of the Black Sea and south of the Danube river, Bulgaria is bordered by Greece and Turkey to the south, Serbia and North Macedonia to the west, and Romania to the north. It covers a territory of 110,994 square kilometres (42,855 sq mi) and is the 16th largest country in Europe. Sofia is the nation's capital and largest city ; other major cities include Burgas , Plovdiv , and Varna .
Bulgaria has an upper-middle-income economy , ranking 70th in the Human Development Index . Its market economy is part of the European Single Market and is largely based on services, followed by industry—especially machine building and mining—and agriculture. The country faces a demographic crisis; its population peaked at 9 million in 1989, and has since decreased to under 6.4 million as of 2024. Bulgaria is a member of the European Union , the Schengen Area , NATO , and the Council of Europe . It is also a founding member of the OSCE and has taken a seat on the United Nations Security Council three times. (Full article... )