A voting system (also referred to as an electoral system) or voting theory, allows voters to choose between options, often in an election where candidates are selected for public office. Voting can be also used to award prizes, to select between different plans of action, or by a computer program to find a solution to a problem. Voting can be contrasted with consensus decision making and hierarchical or authoritarian systems.

A voting system contains rules for valid voting, and how votes are aggregated to yield a final result. The study of formally defined voting systems is called voting theory, a subfield of political science, economics or mathematics. Voting theory began formally in the 18th century and many proposals for voting systems have been made.

Voting systems are either majority rule, proportional representation or plurality voting with a number of variations and methods such as first-past-the-post or preferential voting.

With majority rule, those who are unfamiliar with voting theory are often surprised that another voting system exists, or that "majority rule" systems can produce results not supported by a majority. If every election had only two choices, the winner would be determined using majority rule alone. However, when there are three or more options, there may not be a single option that is preferred by a majority. Different voting systems may give very different results, particularly in cases where there is no clear majority preference.