A swing voter is someone who lacks a strong affiliation with a particular political party. As a result, the voter's behavior in an election is not easy to predict; the voter may cross party lines, for example, or decide to abstain from voting altogether. Many political campaigns expend a great deal of effort in trying to win the hearts and minds of swing voters, in the hopes of influencing the outcome of the election. In Presidential races in particular, swing voters are a crucial part of the electorate in so-called “battleground states,” where the election could go either way.

It is common to confuse a swing voter with an undecided voter. In fact, many swing voters are undecided voters, but there are some subtle and important differences between these two groups of voters. Undecided voters are voters who are unsure about how they plan to vote in the election, making them open to input from any campaign. Many undecided voters are new voters, who have not yet established their own personal political philosophy.

While a swing voter can be undecided, his or her defining characteristic is a lack of willingness to commit to a particular party. Some common types of swing voters include conservative Democrats, who may vote Republican if they don't like the Democratic candidate, and liberal Republicans, who may choose to vote Democratic if they feel that the Republican candidate is too conservative. While these are the most well known swing voters, swing voters can be found in other parties as well, and some politicians also identify swing voters by race, gender, and socioeconomic class in addition to politics.

For example, Hispanic populations are often viewed as a major factor in the swing vote. While the early 21st century demonstrated a marked shift in the direction of the Democratic party for Hispanics in the United States, the Republican party is well aware that many of these swing voters could be wooed back with the right candidate and policy recommendations. Political parties also focus on blocks of swing voters in particular socioeconomic classes in the hopes of expanding their voting base.

Winning the swing vote is a very important aspect of a successful political campaign. In addition to helping the candidate win the election, a sweep of the swing vote can also indicate that the candidate is flexible, strong, and a valuable asset to his or her party. Political analysts working for political campaigns tend to invest a great deal of energy, therefore, in identifying the swing vote and figuring out how to secure it, sometimes working swing voter by swing voter to turn the tide of opinion.