Cyclophilin B, also known as CypB or PPIB, is an enzyme that belongs to the family of peptidyl-prolyl isomerases (PPIases). It plays a vital role in protein folding, a process that is essential for the proper functioning of proteins within the cell. Cyclophilin B is involved in various cellular processes, including the immune response, and has been implicated in the pathogenesis of several diseases, such as cancer and viral infections. In the context of viral infections, Cyclophilin B has been shown to interact with the hepatitis C virus (HCV) NS5B polymerase, enhancing its RNA-binding activity, which is crucial for viral replication. Inhibitors of cyclophilin B have demonstrated antiviral activity against HCV, both in vitro and in vivo, suggesting a potential therapeutic target for the treatment of HCV infection. Moreover, Cyclophilin B has been reported to be overexpressed in various cancers, including non-small cell lung carcinoma, hepatocellular carcinoma, and pancreatic carcinoma. Its overexpression has been correlated with reduced patient survival, indicating a possible role in tumor progression.