Bacteriophages (phages) are viruses of bacteria that can kill and lyse the bacteria they infect. After their discovery early in the 20th century, phages were widely used to treat various bacterial diseases in people and animals. After this enthusiastic beginning to phage therapy, problems with inappropriate use and uncontrolled studies and ultimately the development of antibacterials caused a cessation of phage therapy research in the West. However, a few institutions in Eastern Europe continued to study and use phages as therapeutic agents for human infections. The alarming rise in antibacterial resistance among bacteria has led to a review of the Eastern European studies and to the initiation of controlled experiments in animal models. These recent studies have confirmed that phages can be highly effective in treating many different types of bacterial infections. The lethality and specificity of phages for particular bacteria, the ability of phages to replicate within infected animal hosts, and the safety of phages make them efficacious antibacterial agents. Although there are still several hurdles to be overcome, it appears likely that phage therapy will regain a role in both medical and veterinary treatment of infectious diseases, especially in the scenario of emerging antibacterial resistance.