This research addresses the processes of party change. In a theoretical dimension, we intend to test the models indicated by Panebianco (1982), Harmel and Janda (1994) and Gauja (2017), to propose a new heuristic for the study of party change. The proposition of an “integrative model” of party change seeks to combine causality analysis, typical of process tracing methodologies, and models of organizational change based on internal/external stimuli. The empirical dimension of the research will deal with the case of the Partido Socialista Brasileiro (PSB) and the self-reform process experienced by this organization between 2019 and 2022. The context of the party's formation, still in the 1940s, and its organizational characteristics and functional performance, will be studied, as well as the contemporary context of the party, between 2000 and 2022, from an electoral and organizational perspective. The contextual analysis will be associated with the collection of qualitative data from PSB members who have experienced the self-reform process. The combination of sources will allow the construction of a model of causal processes between environment and organization.