The “party system” is the whole of political parties in a certain State and the elements which characterize its structure: the number of parties; the relations among them, consideration of their magnitude as well as their relational forces, their ideological and strategic locations, are all elements to determine the ways of interaction and the nature of relations.

With respect to the number of political parties existing in a given political system, reference is made to multipartisanship, bipartisanship, or unique party. Regarding dictatorial or totalitarian forms of government, it can be said of a unique party system (as it happened in the fascist regimes, or Communist China or the Soviet Union) that it is not about institutions derived from a democratic process, but rather structures for power preservation.

Bipartisanship (as in the United States and England, for example) is identified as derived from an electoral system based on a majority principle, while the multipartisanship system (such as in Germany, Belgium, Finland, The Netherlands and Switzerland) is identified as an effect from the proportional representation system. This reductionist way of analysis establishes a line of connection between fragmentation (multipartisanship-proportional representation) and polarization (bipartisanship-majority), which has made to consider that either one system or the other contributes to the crisis and lack of stability of the democratic system.

Other criteria disregard quantitative typology in order to favor competition or are not within the political party system.