A single-issue party is a political party that only campaigns on one issue. Such a party is rarely successful in gaining elected office.

It is generally believed that single-issue parties are favoured by voluntary voting systems, as they tend to attract very committed supporters who will always vote. Through systems like instant runoff voting and proportional representation they can have substantial influence on the results of elections. First past the post voting systems tend to nullify their influence.

Some examples are the former Greedy 40% Extra party formed to protest against the increase in politician wages, and the Bloc Québécois party in Canada, formed to call for the separation of Quebec. Green parties and Marijuana Parties, which exist in a number of countries were based around single issues. These parties often evolve to adopt a full platform, however, and most Green Parties and today's Bloc have full platforms. In the case of the Bloc, separatism is today a secondary issue.

See also: single issue politics.