Furcation involvement (FI) is the lesion and destruction of periodontium that spread to the root furcation of multi-root teeth, where periodontal pockets, loss of periodontal attachment and resorption of alveolar bone are formed. Furcation involvement is a common concomitant lesion of periodontitis. The severity of furcation involvement can directly affect the prognosis of periodontitis. However, the specificity of the anatomical structure of the root furcation greatly increases the difficulty of treatment. Therefore, early detection and treatment of furcation involvement is crucial for the prevention and control of periodontitis. This paper briefly describes the pathogenesis of furcation involvement and discusses the diagnosis, classification and treatment of this disease, which is helpful to improve the clinical diagnosis and treatment of furcation involvement.