Phage T4 is a large DNA virus that infects and multiplies in the bacterium Escherichia coli (E. coli) and certain other bacteria that normally inhabit the mammalian gut. Relatives of T4 are widely distributed in nature and propagate in a variety of bacterial species in marine and terrestrial environments. The genomes of these phages encode an enormous biochemical complexity that rival the complexity exhibited by the much larger genomes of their bacterial hosts. Collectively, T4 and its relatives have proven to be powerful systems for research into the genetic and biochemical mechanisms that control the replication, expression and evolution of DNA genomes as well as viral assembly. This book contains a collection of review articles covering research in these areas over the last 20 years. The articles appeared online as a thematic series in 2010 in BioMed Central’s Virology Journal. They are reprinted here in hardcopy as a convenient source of the most current reviewed information on this family of phages for instructors and trainees in the microbial and molecular biological sciences.