An organized group that has as its fundamental aim the attainment of political power and public office for its designated leaders. Usually, a political party will advertise a common commitment by its leaders and its membership to a set of political, social, economic and/or cultural values (an ";ideology";) that distinguish it from other political parties and which supposedly provide the basis for the policies the party proposes to implement or maintain through its members who obtain public office. A political party differs from a pressure group in that a pressure group is primarily interested in influencing whatever government officials actually happen to be in office rather than in attaining office for its own leaders, and accordingly interest groups do not normally put forward candidates for public office under their own name (although they may sometimes endorse particular candidates put forward by party organizations). In a democracy, political parties primarily function as agencies for recruiting suitable candidates to run for elective office and for organizing and conducting election campaigns. They may also become important in selecting candidates for appointive political office when winning the election has provided the party's leaders with power to appoint new officials to the cabinet and other top policy-making positions in the government bureaucracy.

Political parties may also have another function as vehicles for coordinating the day to day activities and policy decisions of their elected and appointed office-holders so as to fulfill the party's policy platform, as for example, through an organized party caucus and a full-time party leadership machinery in the parliament or other legislative assembly. However, unless the national party organization is in a good position to reward its members for ";voting the party line"; after they have been elected to office or to punish them for failing to support the party platform, the party organization's preferences may often not be the most important influence on the policy decisions made by its supposed representatives. In the United States, neither the Democrat nor the Republican national convention (nor their standing national committees) have the power to deny renomination to their parties' uncooperative representatives in Congress so long as they can win renomination in local party primaries or party conventions back home in their states or districts. The national party organizations' financial contributions to the campaign expenses of Congressional candidates (and usually those of state and local party organizations as well) tend to account for only a rather small proportion of what candidates need to be re-elected, so the party leaderships' financial leverage over their parties' office holders tends to be quite limited as well. The dominant role of ";seniority"; in guaranteeing individual committee assignments and personal influence in the House and the Senate, as well as the fact that the House and Senate party leaderships are elected by their own House and Senate party caucuses rather than appointed by the national party organization, considerably insulate ";non-conformist"; representatives from retaliation by their national party organizations.