Accurate evaluation of electoral systems requires precise measurement of both the disproportionality and the concentration of party systems. While the measurement of disproportionality has been investigated systematically and clear guidance for measurement exists, such treatment is lacking for the concentration dimension. This paper clarifies the theoretical concept of concentration in focusing on the directness of the voter-government link and differences between types of coalitions. In light of this concept, a new measure is introduced, and the different measures are compared theoretically as well as empirically. In conclusion, the effective number of parties measure provides a fruitful framework, but should be applied to the cabinet instead of the parliament level in order to clearly identify substantial features of party system concentration.