A single-issue party is a political party that only campaigns for one issue. They are rarely successful in gaining elected office. It is generally believed that they are aided by voluntary voting systems, as they tend to attract very committed supporters who will always vote, and through systems like instant runoff voting and proportional representation they can have substantial influence in 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.