- Democratic congressional and state primaries: open
- Republican congressional and state primaries: open
- Democratic Presidential primary: open
- Republican Presidential primary: open
- Montana has nonpartisan registration. There is no option to affiliate with a political party on the voter registration form.
Details of voting in congressional and state primary elections:
- Voters do not declare affiliation with a party in order to vote, but they must choose one party's ballot.
- Voters are given all the parties' ballots, and can choose in private which party ballot they wish to vote. Voters in a primary election cannot vote more than one party's ballots.