European Union. The European Union (EU) is a political and economic union of 27 member states that are located primarily in Europe. A supranational union with a total area of 4,233,255??km2 (1,634,469??sq??mi) and an estimated population of over 450??million as of 2025, its member states generated a nominal gross domestic product (GDP) of around ???18.802 trillion in 2025, accounting for approximately one sixth of global economic output. The EU is often described as a sui generis political entity combining characteristics of both a federation and a confederation.