The main goal of this study is to collect post marketing data from patients with chronic hepatitis D virus (HDV) infection who are treated with bulevirtide to describe the long-term effects of bulevirtide treatment and evaluate the safety of participants treated with bulevirtide.

The study design time perspective is retrospective and prospective for participants who previously participated in MYR-Reg-02 and are currently receiving BLV and prospective for participants who are scheduled to receive BLV.

Key Inclusion Criteria:

• Individuals who have been diagnosed with chronic hepatitis D virus (HDV) infection for at least 6 months before study enrollment, confirmed by respective documentation in the individuals' medical records.
• Must have the ability to understand and sign a written informed consent form, which must be obtained prior to initiation of study procedures.
• Must be willing and able to comply with the visit schedule and study requirements.
• Cohort 1 only: Must have participated in study MYR-Reg-02.
• Cohort 2 only: Individuals scheduled to receive bulevirtide (BLV) according to the approved label or for whom the decision to start treatment with BLV according to the approved label has been made and treatment initiation is planned.

Key Exclusion Criteria:

• Individuals currently enrolled in BLV clinical treatment studies and/or other interventional clinical studies with an investigational agent.
• History or current presence of clinically significant illness or any other major medical disorder that may interfere with individual follow-up, assessments, or compliance with the protocol.
• Coinfection with hepatitis C virus (HCV) or human immunodeficiency virus (HIV) (Individuals with HCV antibodies can be enrolled if HCV RNA is negative).
• Solid organ transplantation.
• Any history, or current evidence of clinical hepatic decompensation (ie, ascites, encephalopathy, jaundice, or gastrointestinal bleeding (GIB)).
• Presence of hepatocellular carcinoma (HCC) as evidenced by imaging (eg, ultrasound or computed tomography scan) performed within 4 months prior to Day 1 for individuals with cirrhosis and within 6 months prior to Day 1 for individuals without cirrhosis.
• Pregnant or breastfeeding females.
• Individuals with a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection confirmed by a positive polymerase chain reaction test result.
• Known hypersensitivity or contraindication to BLV or formulation excipients.
• Individuals who are committed to an institution by virtue of a court or official order.
• Individuals deemed by the study investigator to be inappropriate for study participation for any reason not otherwise listed. This includes persons dependent on the sponsor, investigator, or trial site.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.

This study will enroll participants who participated in Study MYR-Reg-02 or are scheduled to receive BLV according to the approved product label and not currently enrolled in a clinical treatment study.