Approximately 600 patients with locally advanced, unresectable ESCC (AJCC 8th cStage II-IVA) will be randomized in a 2:1 ratio to receive either durvalumab + dCRT or placebo + dCRT. The primary objectives of this study are to assess the efficacy of durvalumab + dCRT compared with placebo + dCRT in terms of progression free survival (PFS, per RECIST 1.1 as assessed by BICR) in PD-L1 High population.