When democracies ban political parties, one of the central issues that usually emerges in both public and academic debate concerns the effects of proscription. Some argue that proscription may lead to radicalisation, a growth of militancy and readiness to use violence. Others argue that, in the long run, banning parties may damage the foundations of a democratic polity as the ban may be interpreted as a silent weakening of democratic rights in the state and therefore a failure of democracy itself. However, and notwithstanding its centrality for the conduct of democratic politics, the impact of party bans on party system development has remained mostly under-researched. Trying to address this lacuna, and employing a new dataset of banned parties in Europe between 1945 and 2015, the study reported in this article compares the effects of party ban regulation on party system stability in three different arenas: electoral, parliamentary and governmental. In particular, the impact of party proscription on electoral volatility, fragmentation and closure is examined in three countries: Turkey, Germany and Spain. Using examples both at national and regional (e.g., Basque Country, Navarre, Saxony) levels, and making use of survey data when available, it is found that the banning of a relevant political party not only increases volatility and reduces fragmentation, but also alters the existing structure of competition at the time of government formation. Likewise, the empirical analysis also suggests a number of alternative hypotheses (i.e., organisational succession, electoral system) when trying to explain why the outcomes of some cases within each country deviate from theoretical expectations. Finally, the article also examines the phenomenon of ‘non-banning’ and how the failure of attempts to ban political parties might affect the development of a party system.