A swing voter is a voter who may not be affiliated with a particular political party (independents) or who will vote across party lines. Examples include "Reagan Democrats" who voted for Ronald Reagan in the 1980s.

Optimists believe that swing voters will typically vote for the candidate who best suits their needs or the issues that they believe in. Realists recognise that swing voters actually possess few convictions or beliefs that would commit them to one party or another, and in reality allow their voting choice to be influenced by the press or their neighbors. Pessimists think that swing voters are too impulsive to be relied on as a political group, and portray them as reckless, unpredictable and a waste of time.

While the swing voter is ostensibly the target of most political activity during elections, the political parties know that the shift from one party to another is dependent only to a small extent on swing voters. Much more important than the swing voter is the ability of one party in comparison to another in getting out its core support. As people become disillusioned with their favoured party, they are more likely to abstain than switch.

The 2004 US presidential election was notable for the extent to which the Bush campaign was successful in getting out its vote. Republican strategists argued that it would be a mistake to play for the centre ground, i.e. swing voters, and that they needed to put all their effort into energising their natural support.

See also Swing (politics).