The European Union is a political and economic union of 28 member states that are located primarily in Europe. Its members have a combined area of 4,475,757 km² and an estimated total population of about 513 million. The EU has developed an internal single market through a standardised system of laws that apply in all member states in those matters, and only those matters, where members have agreed to act as one. EU policies aim to ensure the free movement of people, goods, services and capital within the internal market, enact legislation in justice and home affairs and maintain common policies on trade, agriculture, fisheries and regional development. For travel within the Schengen Area, passport controls have been abolished. A monetary union was established in 1999 and came into full force in 2002 and is composed of 19 EU member states which use the euro currency. The EU and European citizenship were established when the Maastricht Treaty came into force in 1993.