The use of bacteriophages (phages) to treat bacterial infections, known as phage therapy, has a history substantially longer than that of antibiotics, yet these drugs have been the treatment of choice in the West for over 60 years owing to efficacy, low toxicity and ease of production. Bacteria are becoming increasingly resistant to antibiotics while efforts to discover new agents have drastically reduced. Phages have co-evolved with their hosts over billions of years and have acquired mechanisms to counter bacterial defences such as extracellular biofilm production, which severely reduces the effectiveness of conventional antibiotics. Recent animal and human trials show phages to be safe, well-tolerated agents with a bright future as an alternative to chemical agents.