Many West-European parties have responded to a changing and challenging environment by adopting multiple party reforms. In this article, we propose a comparative framework to study party reforms based on an adaptation of Harmel and Janda’s (1994) Integrated Theory of Party Goals and Party Change and its application to three diferent features of party action. We argue that the causes leading to reforms are multiple and difer according to the nature of these diferent features (i.e. programmatic-, personnel- and organization feature). FsQCA analyses show that the three types of reforms implemented by the six mainstream Belgian parties between 1987 and 2014 are all explained by fundamentally diferent complex causal pathways and that not a single causal condition considered was sufcient in itself to predict party reforms. Hence, we argue that the literature should now extend in two complementary directions. First, we suggest moving away from considering party reforms as only explained by separate conditions, since those are always the result of a combination of causal conditions. Second, we highlighted that it is not possible to commonly explain diferent types of reforms without stressing that only a diversity of (combinations of) causes allows to do so. Future research should better link the nature of the reforms undertaken to the diferent causes that may push parties to adopt them. ; info:eu-repo/semantics/published