Cyclophilins (Cyps) are proteins that are ubiquitously present with peptidyl-prolyl cis-trans isomerase activity and play an important role in de novo protein folding and in isomerization of native proteins in several cellular systems. There is growing evidence that indicates CypB is a positive modulator of the HCV RNA-dependent RNA polymerase in the replication complex. Early in vitro and animal data with selective Cyp inhibitors show a potent anti-HCV effect. This anti-HCV effect was confirmed in the first patient study with the selective Cyp inhibitor Debio-025. Preclinical data suggest that Cyp inhibitors may present a higher barrier to the selection of resistance than protease and polymerase inhibitors and that a combination of Cyp inhibitors with either of these drugs or interferon results in additive or synergistic anti-HCV activity. By interfering at the level of host-viral interaction, Cyp inhibition may open the way for a novel approach to anti-HCV treatment that could be complementary, not only to interferon-based treatment, but also to future treatments that directly target HCV replication enzymes such as protease and polymerase inhibitors.