A virus is an infectious agent capable of multiplying inside the living cells of an organism. Virology is the scientific discipline focused on the study of viruses. Focused on viruses, this discipline comprises the study of their physiology, evolution, interactions, structure, clinical aspects, and ecology. Viruses come in diverse forms which points towards the need to organize them. This is achieved through virus classification, where they are grouped based on various characteristics. One way is classifying them based on their host, like animal viruses or plant viruses. Virology delves beyond classical viruses, encompassing even smaller and less complex entities like viroids and satellites. This field primarily focuses on viral diseases, which arise when pathogenic viruses or related particles invade an organism. Familiar examples include the common cold, HIV/AIDS, and parainfluenza virus infections. This book provides comprehensive insights into the field of virology. The topics covered in this extensive book deal with the core aspects of this field. Coherent flow of topics, student-friendly language and extensive use of examples make this textbook an invaluable source of knowledge.