It was held on the same day as elections for Northern Ireland's 26 local councils, the Scottish Parliament and Welsh Assembly elections, a number of local elections in England and the United Kingdom Alternative Vote referendum. As in the past, the 2011 election to the Assembly was conducted using the single transferable vote (STV) system of proportional representation. The 108 seats were contested in 18 constituencies by 218 candidates, including 15 independents and the nominees of 14 separate political parties.