This chapter argues that the singular nature of American parties is due to specifically American features, such as: the separation of powers, the plurality electoral system, and differences in American political development that stifled the growth of socialism as a mass political movement in the United States. Political parties are the most critical intermediary political institutions between citizens and government. America's first parties had formed around tensions and disputes leading up to a presidential contest, and it was another such contest in 1824 that led to the creation of the first substantive and durable American political parties. The early classic works on political parties in liberal democracies were written by European scholars based on the European political experience and, as such, generally dismissed the American parties as aberrant. As American politics has become somewhat more polarized and ideological, many comparable democracies have witnessed a decline in class politics and in the public resonance of long-established ideologies.