This reference book offers an in-depth analysis of the fundamental aspects, causative agents, and clinical manifestations of emerging and re-emerging infectious diseases of viral origin (EID-REID). It elucidates the role of evolutionary processes in the emergence, adaptation, and dissemination of pathogens. The initial chapter explores the causative agents behind EID-REID, providing a comprehensive overview of their origins, characteristics, and modes of transmission. The book further presents the structure, pathophysiology, and clinical presentation of various viral pathogens, including notable viruses such as the Crimean-Congo hemorrhagic fever Orthonairovirus (CCHFV), Rift Valley fever virus, Lassa virus, Nipah virus (NiV), Filoviridae, and coronaviruses (MERS, SARS, SARS-CoV-2). Additionally, the book elucidates the multifaceted landscape of treatment strategies, highlighting the pivotal role of pharmacological strategies, investigational drugs, vaccines, and immunomodulatory approaches. It also underscores the importance of clinical examination, immunoassays, and molecular diagnostic techniques for the early detection and accurate diagnosis of viral EID-REID. Toward the end, the book sheds light on the pivotal role of the Ayurveda, homoeopathic system of medicine, medical nutrition therapy, computational biology, bioinformatics, and systems biology in advancing disease management paradigms. This book is intended for epidemiologists, virologists, infectious disease specialists, and other healthcare practitioners who seek in-depth knowledge about emerging and re-emerging infectious diseases.