This article focuses on the transformations of Algerian Islamist parties, placing them in a dynamic context. Having undergone both phases since the fall of the ruling party in 1989, Algeria furnishes a case study for analyzing the conditions and challenges of the inclusion and exclusion of Islamist parties. The synchronic and diachronic construction of the Algerian case, combined with a comprehensive and inductive approach, thus allows us to contribute to the inclusion-moderation debate on multiple empirical, methodological, and conceptual levels. Only this dual approach makes it possible to grasp the changes and continuities in the ideology and modes of action of the Islamist parties as well as the evolution of how the regime integrated or excluded them from the political arena. On the level of defining moderation and radicalization, it allows us to differentiate between, on the one hand, political labelling by the various Islamist or non-Islamist actors and institutionally defined legal criteria and, on the other hand, academic concepts. This calls for adopting a dual analysis: what we term a radicalization within the institutional arena (by subverting the foundations of the state, i.e., the Islamic state project) and a radicalization from outside it (by armed violence). In this framework, the political exclusion of an Islamist party correlates closely not with its intrinsic radicality but with the crossing of an electoral threshold, which sets the stage for implementing its radical program. Knowing how the civilian and military authorities assess this threat is thus essential for understanding the exclusionary and inclusionary processes. Next, we must differentiate between inclusion in the electoral game, which is accepted, and inclusion in the executive branch, on which the Islamist parties are internally conflicted. Finally, it behooves us to show that the moderation of programs and modes of action does not stem from (prior) inclusion in the political game, but instead results from a new institutional constraint. It produces specific effects, namely partisan fragmentation, and ambivalence about the identity of Islamist parties.