Iridoviruses refer to a type of double-stranded DNA viruses with an icosahedral structure that belong to the iridoviridae family. The members of this family can infect invertebrates, protozoa, vertebrates and algae. The host range of iridoviruses differs, such as some have a broad range of hosts, while others are limited to a small number of hosts. Non-lethal and concealed infections are common in various hosts. Horizontal transmission of iridoviruses generally occurs through predation or cannibalism of infected invertebrate hosts. They produce iridescence in the infected tissues and reproduce in the cytoplasm. Iridoviruses infect a variety of animals including reptiles, molluscs, fish, insects, amphibians and crustaceans. These viruses have a distinctive trait which is terminally redundant and circularly permuted organization of the genome. This book aims to shed light on iridoviruses. The readers would gain knowledge that would broaden their perspective about the molecular virology and biology of these viruses. The extensive content of this book provides the readers with a thorough understanding of the subject.