In this study the authors aim to add to the understanding of whether, and if so how, a change of electoral system affects factors such as voter turnout and the party system, and the authors' focus has been on changes that result in mixed electoral systems. They used three country cases (Japan, Italy, and New Zealand) to explore patterns in a before-and-after design. The findings suggest that a country cannot expect a significant effect on voter turnout if it decides to change its electoral system to a mixed system. Regarding party system fragmentation, the results show that the change of the electoral system in New Zealand from a plurality system to a mixed member proportional system had a clear and immediately positive effect on the party system. However, the results do not indicate that the changes of electoral systems in Japan and Italy have had any significant effect on the party system.