This book provides a comprehensive introduction to the field of virology, focusing on the biology of viruses and their interactions with host cells. It covers viral structure, replication, pathogenesis, and immune responses to viral infections. The book also examines the epidemiology of viral diseases and strategies for their prevention and treatment, including vaccines and antiviral drugs. Designed for undergraduate and graduate students, it integrates molecular and clinical perspectives to enhance understanding. Supplementary resources include problem sets, case studies, and access to interactive online content.