Single transferable vote
Single Transferable Vote (STV) is a voting system based on multi-member constituencies. In Ireland, which uses STV, constituencies each have between 3 and 5 MPs. Each party nominates a list of candidates, and voters rank the candidates in order of preference - it is possible for voters to "mix and match" candidates from different parties.
At the count, candidates who reach the necessary "quota" (the number of voters divided by the number of seats, plus 1) are automatically elected; otherwise (as in the Alternative Vote system), the lowest-scoring candidate is eliminated and their votes transferred to other candidates according to second and subsequent preferences. This process continues until all the seats have been allocated.
An additional feature of STV is that votes are also transferred from candidates with more votes than they need to secure election, according to second and subsequent preferences of the people who voted for the winning candidate. Thus, STV does very well at minimizing "wasted" votes, both votes cast for losing candidates and surplus votes cast for candidates who win easily. However, as STV is generally used in smaller electoral districts it does not always guarantee the same proportionality as systems which use larger districts, and in a democracy where many political parties are active, smaller parties may be at a disadvantage similar to their experience under First Past the Post.
STV is used in the Republic of Ireland, Northern Ireland (except for Westminster elections), Malta and for the Senate elections in Australia. It has been used for Scottish local elections from 2007 and was recommended by the Sutherland Commission for local elections in Wales.