Preselection is the process by which a candidate is selected, usually by a political party, to contest an election for political office. It is also referred to as candidate selection. It is a fundamental function of political parties. In countries that adopt Westminster-style responsible government, preselection is also the first step on the path to a position in the executive.

Deselection is the opposite procedure: the political party withdraws support from one of their elected office-holders at a subsequent election. A new candidate must then be selected by that party. The deselected representative is usually free to still contest the election as an Independent or as a representative of another party.

An example of a preselection procedure that gains extensive media coverage is the selection of candidates for President of the United States, referred to by one observer as 'the wildest democratic political bazaar in the world'. These are generally known as presidential primaries, but are actually a combination of primary elections, in which voters in a jurisdiction select candidates, and caucuses, in which candidates are selected by a narrower (but still potentially large) group of party members.

In other countries, a wide variety of preselection systems exist, though the majority involve members of a political party or party executive playing a role in selecting candidates to compete in elections.