Using electoral data from a nearly comprehensive set of the world’s electoral democracies (1992–2014), including 131 independent countries and one non-sovereign territory, this article develops an explanatory model of legislative fragmentation that incorporates electoral fragmentation, the territorial patterns of party support, district magnitude, specific electoral system effects, and the balance of personal and party vote components within the incentive structures generated by electoral rules. The analysis proves that there is a strong negative association between the territorial homogeneity of the vote and legislative fragmentation, and shows that those varieties of electoral rules that increase the salience of personal component in party-centred elections tend to enhance legislative fragmentation. Due to its statistical properties, the model allows for establishing the impact of each of the factors, as well as their relative weights, with a high degree of certainty.