They join other parties in the chamber to give them more power during debates.
Labour join with the Alliance of Socialists and Democrats, The Conservative Party sit with the European Conservatives and Reformists, Green MEPs sit with the Green Party of Europe, UKIP join onto the Party of Freedom and Direct Democracy whilst the one Lib Dem is a member of the Alliance of Liberals and Democrats.
MEPs spend most of their time in Brussels but will come to Strasbourg, roughly once a month, to cast their votes on debates.
The Strasbourg parliament sits close to the border between France and Germany and is a sign of peace and a changed Europe from the days of the 40s and 50s.
Members are paid around £61,000 a year after EU tax, although this may be subject to their own national tax.
They can claim £225 a day in expenses for accommodation and food. Travel costs are covered separately but also work on an expenses system.
The European Parliament discusses a range of issues including foreign affairs, workers' rights, consumer rights and climate change.