Viruses interact with all forms of life and have shaped evolution for 4 billion years. The COVID-19 pandemic highlights the importance of conducting scientific research into viruses to understand the interactions between them and their hosts. Virology is made up of eight chapters, all of which have been written by outstanding female virologists, emphasizing womens fundamental role in all aspects of science. It summarizes our current knowledge about the biology of viruses in general and analyzes the specific features of several ones of medical, veterinary and agricultural importance. Genome replication strategies of different virus families are covered, as well as strategies for survival within their hosts by counteraction of the cellular innate antiviral responses. Attention is also given to viral strategies for efficient dissemination in nature, as well as the evolution of a select group of viruses.