The secret ballot, also known as the Australian ballot, is a voting method in which a voter's identity in an election or a referendum is anonymous. This forestalls attempts to influence the voter by intimidation, blackmailing, and potential vote buying. This system is one means of achieving the goal of political privacy.

Secret ballots are used in conjunction with various voting systems. The most basic form of a secret ballot uses paper ballots upon which each voter marks their choices. Without revealing the votes, the voter folds the ballot paper in half (if necessary) and places it in a sealed box. This box is later emptied for counting. An aspect of secret voting is the provision of a voting booth to enable the voter to write on the ballot paper without others being able to see what is being written. Today, printed ballot papers are usually provided, with the names of the candidates or questions and respective check boxes. Provisions are made at the polling place for the voters to record their preferences in secret, and the ballots are designed to eliminate bias and prevent anyone from linking voters to the ballot.

A privacy problem arises with moves to improve the efficiency of voting by the introduction of postal voting and remote electronic voting. Some countries permit proxy voting, but some argue this is inconsistent with voting privacy. The popularity of the ballot selfie has challenged the secrecy of in-person voting.

In systems of direct democracy, such as the Swiss Landsgemeinde, voting is typically conducted publicly to ensure all citizens can observe the outcome.

By the late 20th century, the secret ballot had become commonplace for "individual citizens" in democracies. Votes taken by elected officials are typically public, so citizens can judge officials' and former officials' voting records in future elections. This may be done with a physical or electronic system or through a roll call vote. Some faster legislative voting methods do not record who voted in which way, though witnesses in the legislative chambers may still notice a given legislator's vote. These include voice votes where the volume of shouting for or against is taken as a measure of numerical support and counting of raised hands. In some cases, a secret ballot is used to allow representatives to choose party leadership without fear of retaliation against those voting for losing candidates. The parliamentary tactics of forcing or avoiding a roll call vote can be used to discourage or encourage representatives to vote in a manner that is politically unpopular among constituents (for example, if a policy considered to be in the public interest is difficult to explain or unpopular but without a better alternative, or to hide pandering to a special interest) or to create or prevent fodder for political campaigns.

Public methods of citizen voting have included:

Private methods of citizen voting have included:

In ancient Greece, secret ballots were used in several situations like ostracism and also to remain hidden from people seeking favors. In early 5th century BC the secrecy of ballot at ecclesia was not the primary concern, but more of a consequence of using ballots to count the votes accurately. Secret ballot was introduced into public life of Athens during second half of the fifth century.