Despite the growing amount of party regulation, we still have a limited understanding of the effect that party laws have on party systems and political competition. Notwithstanding predictions that incumbent parties adopt rules which favour their own position, found in both the cartel party thesis and the rational actor view of politics, we continue to witness the frequent appearance of new political parties, some of which successfully enter parliament. Using comparative electoral data and a newly built dataset on party regulation in post-war Europe, we trace the changes in the rules governing political parties and explore the effect of party regulation on the number of successful new entrants. Overall, we find that more regulation significantly decreases the number of successful new entries, while high electoral volatility and the legacy of post-communism increase the amount of successful new party entries in the legislature. Our nalysis further shows that the existence of public funding and the payout threshold have no effect on the permeability of party systems.