The party system in Malawi has been characterised by instability and fragmentation since the reintroduction of multiparty democracy in 1993. In part this instability is rooted in the legal framework regulating political parties as organisations and the functions that parties perform in a democracy. The article outlines the constitutional and legal framework of political parties. But more important is how regulation of functions such as candidate nomination, campaigning and representation in parliament interacts with the structure of the political system, leading to party system instability. Moreover, the effect of regulation of political parties and their activities is strongly influenced by ‘selective’ application of the formal regulations and weak party organisations. Formal rules meant to strengthen political parties have therefore not functioned as intended.