Europe is the world's second-smallest continent by surface area. Europe is the third most populous continent after Asia and Africa. As a continent, the economy of Europe is currently the largest on Earth and it is the richest region as measured by assets under management. Europe's largest national economy is that of Germany, which ranks world's fifth-largest economy. By the millennium change, the EU dominated the economy of Europe comprising the five largest European economies of the time namely Germany, the United Kingdom, France, Italy, and Spain. In 1999 12 of the 15 members of the EU joined the Euro zone replacing their former national currencies by the common euro. The three who chose to remain outside the Euro zone were: the United Kingdom, Denmark, and Sweden.