Epstein–Barr virus (EBV), also known as Human herpesvirus 4 (HHV-4), infects more than 90% of the global population and establishes lifelong latency in host B lymphocytes. Although primary infection is often asymptomatic, EBV is etiologically linked to infectious mononucleosis, multiple lymphoid and epithelial malignancies, and emerging autoimmune disorders. EBV is carcinogenic due to its established role in cancers such as Burkitt lymphoma, Hodgkin lymphoma, nasopharyngeal carcinoma, and EBV-associated gastric carcinoma. Recent advances in molecular virology, immunology, and epidemiology have refined our understanding of EBV latency programs, immune evasion strategies, and oncogenic mechanisms. Moreover, longitudinal studies have strengthened the causal association between EBV and multiple sclerosis. This review synthesizes updated evidence regarding EBV molecular biology, viral persistence, tumorigenesis, and clinical implications, highlighting current challenges and future directions in prevention and therapeutic development.