Political fragmentation is the fragmentation of the political landscape into different parties and groups, which makes it difficult to deliver effective governance.^[1] Political fragmentation can apply to political parties, political groups or other political organisations.

One aspect of political fragmentation can be measured by effective number of parties.^[2]

Scholars, journalists and politicians have theorized about a number of potential effects of political fragmentation. For example, it has been argued that higher fragmentation allows voters to better represent their political spectrum of political positions. The length of government coalition formation has also been argued to increase with number of parties and decreases with preexisting political groups.^[3] The strength of these effects has been hypothesized to depend on whether it is the government or the opposition that are fragmented.^[4] However, the political fragmentation of parliaments has little causal effect on a number of dimensions of the quality of democracy.^[5]

The veto player theory predicts that higher fragmentation relates to gridlock,^[6] while other literature does not observe increased gridlock.^[7]

The political fragmentation, represented by effective number of parties, is roughly estimated with the seat product model,^[8][9] and increases with district magnitude and assembly size. The Duverger's law predicts majoritarian elections with district magnitude of one favor a two-party system and proportional representation increases the number of parties. In proportional representation, higher electoral thresholds reduce number of parties represented while increasing wasted vote. Fragmentation tends to moves toward an equilibrium, regardless of the type of voting system.^[10]