Political systems in which only two political parties effectively compete for government office. Minor parties may operate in such a system, although in some cases, as in the United States, they may have to surmount significant barriers to be placed on the ballot paper. Some theorists argue that two-party systems offer a superior form of electoral democracy because unless there are only two parties, there can be no guarantee that any party will have a legislative majority, without which government policy is formed on the basis of bargaining between political elites, which is seen as less accessible to popular control. However, in a two-party system much policy formation takes place within the political parties, also away from popular control. Two-party systems are most often found in association with first-past-the-post electoral systems, as in the United States and Britain.

— Wyn Grant

The Concise Oxford Dictionary of Politics. Copyright © 1996, 2003 by Oxford University Press. All rights reserved.