The hepatitis delta virus (HDV) is a defective satellite virus of the hepatitis B virus (HBV), whose envelope it uses to spread. It is therefore found in patients infected with HBV (those who test positive for hepatitis B surface antigen—HBsAg). It is estimated that 12 to 25 million people worldwide are chronically infected with HDV, with hotspots located in sub-Saharan Africa, the Amazon, Eastern Europe, the Middle East, and Asia. Transmission occurs primarily through sexual and parenteral routes. Diagnosis relies on testing for anti-VHD antibodies (Ab) in all HBsAg carriers and quantifying plasma VHD RNA in anti-VHD Ab-positive (+) patients. A reflex test for anti-VHD antibodies in all initial HBsAg-positive cases improves the VHD screening rate, which is currently insufficient in France (26%).HBeAg-positive HBV infection is responsible for the most severe form of chronic viral hepatitis. In France, more than 80% of HBeAg-positive patients were born abroad. Nearly one-third are diagnosed at the cirrhosis stage. HCV is an independent risk factor for hepatocellular carcinoma (HCC) (three times the risk compared to patients with HBV monoinfection). Patients with HCV-positive RNA should be monitored at a specialized center. Current treatment, despite its burdensome nature, reduces the risk of serious clinical complications. It is based on the use, either as dual therapy or monotherapy, of bulevirtide (BLV, entry inhibitor, 2 mg/day, subcutaneous [SC]) and pegylated interferon alpha (180 μg/week, SC). The goal is to achieve sustained HCV RNA negativity. Prolonged treatment (with at least 96 weeks of virosuppression—undetectable plasma viral load) is necessary to prevent relapses upon discontinuation of treatment. All French patients are eligible for inclusion in the ANRS EP01 Hepdelta real-world cohort.As with HBV, several drugs are currently in development, with the goal of increasing the virologic response rate and achieving functional cure of the infection (i.e., loss of HBsAg).