This book will contain a series of solicited chapters that concern with the molecular machines required by viruses to perform various essential functions of virus life cycle. The first three chapters (introduction, molecular machines and virus architecture) introduce the reader to the best known molecular machines and to the structure of viruses. The remainder of the book will examine in detail various stages of the viral life cycle. Beginning with the viral entry into a host cell, the book takes the reader through replication of the genome, synthesis and assembly of viral structural components, genome packaging and maturation into an infectious virion. Each chapter will describe the components of the respective machine in molecular or atomic detail, genetic and biochemical analyses, and mechanism.