This chapter examines the multiple and sometimes complex areas of political parties' key role in system of campaigns and elections. It discusses different conceptions of party to establish a context. The chapter considers some of the major activities parties engage in during campaigns, including the nomination of candidates for office and the different processes that are employed, the parties' fundraising efforts, and the parties' efforts to assist their candidates during a campaign. It examines several important trends that impact parties and that have been driven by parties since the turn of the century. The chapter shows how the 2016 presidential campaign featured a strong antiestablishment theme. It identifies three elements of political parties—party in the electorate, party in government, and party as organization. The most familiar aspect of Key's model, it can be argued, is party in the electorate—each person's identification or connection to the Democratic, Republican, some other party, or no party at all.