The benefit of postoperative adjuvant therapy for patients with resectable esophageal squamous cell carcinoma (ESCC) is not yet supported by high-level evidence. This review analyzes the role of adjuvant therapy by examining the discrepancy between clinical needs and guidelines, its historical evolution, recent advances in high-risk factors, and future outlooks. We provide a detailed discussion of high-risk factors used for patient selection, including lymph node positivity, and for node-negative patients, features such as tumor length, location, T stage, extent of lymph node dissection, differentiation, vascular and neural invasion, laboratory indices, and molecular markers. The goal is to inform the development of individualized precision treatment strategies for resectable ESCC.