What are the main reasons behind the regulation of political parties by contemporary constitutional practices? This article presents a framework for analysis which identifies types of justifications and actors involved in the process of regulation and their further influence on the outcomes of constitutionalisation. The empirical focus is on the revelatory case of Luxembourg, which amended the constitution for the sole reason of giving parties constitutional status. The analysis suggests that the constitutional regulation of political parties depends on their current interests and power status. Additionally, the paper draws attention to the involvement of external actors and to the changing nature of contemporary constitutionalism.