The number of seats a party has in Parliament is determined by the proportion of votes it receives under the party vote at each general election. If any electorate seats are won by a party's candidates, its seats first go to those candidates. Any leftover seats are then given to list candidates, who are elected according to a ranked list of candidates finalised before the election.
Political parties and their funding are regulated in New Zealand by the Electoral Commission in accordance with the Electoral Act 1993.
Outside of elections, parties play an important role in Parliament and in government. Many votes cast in Parliament on proposed laws are cast as party votes, where a party casts a vote on behalf of all its member MPs. Party membership and size also determines the allocation of Parliamentary resources, like Oral Questions and Select Committee membership. It's also a major factor in deciding which party or parties form the Government, and who becomes the Prime Minister or a Minister.
For registered parties, their registered name is shown on this page. Some parties may have adopted different names in a Parliamentary context or for marketing purposes.