Primaries and caucuses differ in the United States electoral process primarily in how they select delegates for the nomination. Primaries are state-level elections where voters cast secret ballots for their preferred candidates, with results determining delegate allocation. In contrast, caucuses involve local gatherings where party members discuss and vote on candidates openly, often leading to a more communal deliberative process. Both systems aim to gauge public support and ultimately select party nominees for the general election, but they engage voters in different ways.