Bacteriophages, also known as phages, are viruses that infect and replicate within bacterial cells. The word "bacteriophage" comes from the Greek word phagein, which means "to devour"

Bacteriophages are the most abundant biological agents on Earth, and are extremely diverse. They are made up of a nucleic acid molecule surrounded by a protein structure. The proteins protect the genetic material and mediate its delivery into the next host cell.