【Abstract】 Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease with high morbidity and mortality. Accumulating evidence shows that bronchiectasis and COPD can coexist or codiagnosis in one patient, naming BronchiectasisChronic Obstructive Pulmonary Disease overlap syndrome (BCOS). This syndrome is a neglected area of research. The epidemiology, mechanisms, risk factors and treatment for these patients are largely unclear, which demands more research.