A swing vote is a vote that is seen as potentially going to any of a number of candidates in an election, or, in a two-party system, may go to either of the two dominant political parties. Such votes are usually sought after in election campaigns, since they can play a big role in determining the outcome.

A swing voter or floating voter is a voter who may not be affiliated with a particular political party (Independent) or who will vote across party lines. In American politics, many centrists, liberal Republicans, and conservative Democrats are considered "swing voters" since their voting patterns cannot be predicted with certainty.

While the swing voter is ostensibly the target of most political activity during elections, another factor is the success of each party in rallying its core support. In a two-party system, those who become disillusioned with their once-favored party are more likely to vote third-party or abstain than cross over.

Smaller groups that use voting to decide matters, such as chambers of parliament and supreme courts, can also have swing voters. The smaller the group, the more power swing voters can have. For example, on a court of seven judges, of which three are committed to each side of a case, the seventh judge may be seen as single-handedly deciding the case.