Yes, most states require that you indicate your party affiliation in order to vote in primary elections. (There are some exceptions.) When you register to vote using our online voter services, you will be automatically informed of your state requirements.
You can register to vote here.
Note: If you have not chosen a party or do not wish to declare your party, please enter an appropriate note, such as "decline to state,” "none,” "nonpartisan," or "undeclared" on your form. The voter registration system will tell you which of these notes to add in accordance with your state's requirements.
Most Secretary of State websites provide further information about which parties allow unaffiliated voters to participate in their primary election. You can find your state’s website by going to the Election Official Directory. Enter your state and jurisdiction, click "submit," and on the following page click the "Address Information" tab.
You do not need to declare your party affiliation if you only plan to vote in the November general election, but not in the primary election.