Outdated virological response terms used at key trial timepoints in clinical trials with first-generation direct-acting antivirals plus pegylated interferon and ribavirin have failed to keep pace with hepatitis C virus (HCV) drug development. A more intuitive and flexible nomenclature capable of adapting to continuing advances in HCV drug development is needed. Assistance in standardization of the field was provided by members of the Hepatitis C Virus Drug Development Advisory Group, a project of the Forum for Collaborative HIV Research with participation from the American Association for the Study of Liver Diseases, European Association for the of the liver, and the Infectious Diseases Society of America. Our proposed descriptive, virological response nomenclature for key decision points in trials (with and without lead-in treatment) is based on an assay-specified lower limit of quantitation cutoff. This allows responses to be categorized as either quantifiable or unquantifiable HCV RNA, with unquantifiable responses further divided based on whether target HCV RNA was detected or not detected. The unified reporting recommendations will facilitate interpretation of results across clinical trials and validation of new response-guided timepoints. As time-critical treatment parameters are shortened in HCV trials, the proposed nomenclature will greatly simplify and facilitate future adaptations of virological response terms. Our proposed nomenclature will also be helpful in developing treatment guidelines for use in clinical practice. (HEPATOLOGY 2012;56:2398–2403)