[en] In order to grasp the complexity of merger process (Pettigrew, 1990; Van de Ven, 1992; Bergh and Holbein, 1997; Stahl et al., 2013), we analyze institutional logics (Greenwood et al., 2011) at stake from pre-merger phase to post-merger phase (Stahl et al., 2005; Stahl et al., 2013). We conducted an in-depth longitudinal study focused on the merger process of two listed companies in the French urban planning sector. We highlight two main phases: in the pre-merger phase, the organizations dealt with coexistence within institutional logics and ultimately found a strategic solution through a merger (1) and, in the post-merger phase, the institutional logics were combined to shape new strategic choices (2). We found that the relative dominance of the institutional logics at play during the pre-merger step (Phase 1) evolved toward the combining of these logics during the post-merger integration phase (Phase 2).