An extensive literature documents and theorizes the “moderation” of Islamist parties (Schwedler 2011). The issue has gained importance now that elected Islamist parties are leading governments or governing coalitions in Egypt, Tunisia and Morocco, and may do so in other Arab countries undergoing democratic transitions. The literature falls short, however, with its simplistic unicausal explanations of the mechanisms and factors leading to change. In this paper, we thoroughly explore the factors that explain change in the positions, discourses and attitudes of the Tunisian al-Nahdha Party on social, economic and foreign policies. We argue based on field research in Tunisia that the factors leading to change vary across the developmental phases of the history of the party as well as policy issues, and are much more complex than the literature on “moderation” indicates. We identify the causal processes of change at each of the four distinctive phases of the Tunisian al-Nahdha’s history (formative period under the MTI designation, being prevented from participating in elections, outright persecution, and governing after the Jasmin Revolution) by testing existing hypotheses and several more we developed. To test hypotheses of change in the positions of the organization, we conducted twenty-five semi-structured interviews with party leaders, activists, allies and opponents; met with groups of activists; observed operations at the party’s headquarters for three days; and analyzed samples of the party’s archives, internal newsletters and electronic exchange boards. We find that al-Nahdha, and presumably other Islamist parties that value using ijtihad in their jurisprudence are considerably influenced by ideas from non-Muslim sources and by their ideological rivals, and that their positions are heavily path-dependent. We contextualize our findings based on additional field research in Cairo and Lebanon, as well as secondary sources.