Collection of Plasma and Serum Samples From Individuals Initiating Sofosbuvir for Chronic Hepatitis C for Testing

Inclusion Criteria: * The subject is chronically infected with HCV genotypes 1, 2, 3, 4, 5, and/or 6 as documented in the subject's medical records and is naïve to HCV treatment (treatment naïve). * Chronic HCV (with or without HIV \[human immunodeficiency virus\] co-infection) will be documented with historical record of: * A positive HCV RNA test result (result generated at least 6 months before the baseline visit) * A HCV genotype test result (result generated at least 6 months before the baseline visit) * A liver biopsy report demonstrating chronic HCV ---The subject is initiating antiviral therapy with a sofosbuvir regimen as indicated below: * Sofosbuvir plus peginterferon and ribavirin for 12 weeks (peginterferon eligible genotype 1, 4, 5, or 6) * Sofosbuvir plus ribavirin for 12 weeks (genotype 2) * Sofosbuvir plus ribavirin for 24 weeks (peginterferon ineligible or unwilling genotype 1 or genotype 3) * The subject is at least 18 years of age at the time of enrollment * Adequate medical records are available for collection of protocol-defined demographics, baseline patient characteristics, medical history, virology and specific laboratory results, and other information to verify enrollment criteria * The subject and/or legally authorized representative is willing and able to provide consent prior to providing a specimen(s) Exclusion Criteria: * Subjects with history or evidence of decompensated liver disease * Subjects with severe renal impairment or end stage renal disease * Subjects who are not naïve to HCV therapy with prior exposure to an approved or experimental HCV antiviral therapy * Subject has characteristics that are contraindicated in the FDA approved label for sofosbuvir (eg, subjects with contraindications applicable to peginterferon and/or ribavirin, pregnant woman or men whose female partners are pregnant; Sovaldi Package Insert 2013) * Subject is receiving treatment pre- or post-transplant * Subject is unsuitable for study participation based on the Investigator's decision (eg, unlikely to comply with study visit schedule, significant medical complication) * Participating in another investigational study that the Investigator believes might interfere with the subject's participation in this study