Elections in Luxembourg are held to determine the political composition of the representative institutions of the Grand Duchy of Luxembourg. Luxembourg is a liberal representative democracy, with universal suffrage guaranteed under the constitution. Elections are held regularly, and are considered to be fair and free. Separate elections are held to elect representatives at municipal, national and European levels. The main institution to which members are elected is the Chamber of Deputies, the national legislature and the sole source of membership, confidence and supply of the government. Luxembourg is represented by six MEPs to the European Parliament, who are elected simultaneously with elections held in other European Union member states. The country has a multi-party system, traditionally defined by the existence of three large political parties: the Christian Social People's Party (CSV), the Democratic Party (DP), and the Luxembourg Socialist Workers' Party (LSAP). Historically, the three parties have won a large majority of the votes between them, but their total percentage has fallen recently, such that two additional parties, the Greens and the Alternative Democratic Reform Party (ADR) have recorded over 9% of votes at each of last two legislative elections. The CSV (and its predecessor) has provided the Prime Minister for all but 12 years since 1918, and has always been the largest party in the legislature. In this respect, Luxembourg has certain features of a dominant-party system, although coalition governments are the norm and the two most recent governments do not involve the CSV. Luxembourg's electoral system operates on the basis of compulsory voting, with a few exceptions. Luxembourg citizens aged under 75 years who reside in Luxembourg are required to vote, unless they reside in a different municipality from the one in which they are called to vote. Luxembourg citizens aged over 75 years, as well as Luxembourg citizens of any age who do not reside in Luxembourg, are not required to vote.