AbstractBiliary tract cancer (BTCs) is a heterogeneous malignancy divided into cholangiocarcinoma, gallbladder cancer, and ampullary cancer. Due to little or no symptoms, most patients with BTCs are diagnosed with unresectable or metastatic disease. Only 20%–30% of all BTCs are suitable for potentially resectable diseases. Although radical resection with a negative surgical margin is the only potentially curative method for BTCs, most patients develop postoperative recurrence, which is associated with poor prognosis. Therefore, perioperative treatment is necessary to improve survival. There are very few randomized phase III clinical trials of perioperative chemotherapy due to the relative rarity of BTCs. Adjuvant chemotherapy with S‐1 for patients with resected BTC significantly increased overall survival compared with upfront surgery in a recent ASCOT trial. In East Asia, S‐1 is currently considered the standard adjuvant chemotherapy, while capecitabine may still be used in other areas. Since then, our phase III trial (KHBO1401), gemcitabine and cisplatin plus S‐1 (GCS) has become the standard chemotherapy for advanced BTCs. GCS not only improved overall survival but demonstrated a high response rate. The efficacy of GCS as a preoperative neoadjuvant chemotherapy for resectable BTCs has been investigated in a randomized phase III trial (JCOG1920) in Japan. In this review, we summarize the current and ongoing clinical trials focusing on adjuvant and neoadjuvant chemotherapy for BTCs.