This project analyzes how hospital mergers, market concentration, and inter-hospital competition affect healthcare quality in France. It combines a theoretical model of patient behavior at emergency departments—based on Deffains & Doriat-Duban (2001)—with an empirical evaluation of mergers’ impact on service differentiation and hospital performance. The 2023 Emergency Survey by DREES, particularly the “Patient” and “Structure” datasets, is key to modeling waiting times and care pathways across 719 emergency units. Access to the “Patient” data via CASD is essential to link market concentration (e.g., HHI) with quality indicators such as waiting times and readmission rates. This research provides new insights into how organizational decisions shape patient care under growing pressure on emergency services and informs public regulation of unplanned care delivery.