European economic integration began in 1952 when Belgium, France, (West) Germany, Italy, Luxembourg, and the Netherlands founded the European Steel and Coal Community which, with the Treaty on the European Union in 1993, became the European Union (EU). The “free movement of workers” stipulated in Article 45 of the Treaty on the Functioning of the EU represents one of the key pillars of economic integration within the EU, complementing freedom of movement of goods, services, and capital. The principle of free labor mobility enables citizens of an EU member state to enter the territory and labor market of other member states to seek and accept employment and, in effect, to gain access to employment-attached social benefits. The Treaty on the European Union, Directive 2004/38/EC, and the Case Law of the European Court of Justice extend the right of free movement to all citizens of the EU, as well as to their close family members, provided that they do not pose an undue burden for the host country's public funds and that they possess comprehensive health insurance. In 2008, about 2.59 percent of the EU population was born in another EU country (own calculations / EU SILC 2008).