BackgroundBacteriophages were discovered just over 100 years ago and have been used to treat bacterial infections in animals since the 1920s. The antimicrobial resistance crisis has led to a new surge of interest in the use of bacteriophage therapy as an alternative or supplement to antimicrobial therapy in humans and other animals.ObjectivesTo describe the nature of bacteriophages and provide a critical review and update on the clinical use of bacteriophages in the treatment of challenging bacterial infections, with an emphasis on companion animal veterinary applications.Methods and materialsThe scientific literature on the subject was critically evaluated. Findings from the most pertinent papers have been presented in summary form and critiqued.ResultsOver the last 20 years there has been a considerable increase in the volume and quality of publications dealing with bacteriophage therapy. Some recent papers build on excellent work published in the 1980s and describe promising veterinary applications. Challenges related particularly to the registration and approval of phage remedies will need to be overcome before phage therapy can become a mainstream tool for use in veterinary settings. Considerably more research, particularly controlled clinical trials, needs to be done.Conclusions and clinical importanceBacteriophage therapy is one of the most promising approaches to tackling the looming antimicrobial resistance crisis, yet substantial regulatory challenges will need to be overcome before it enters widespread use. Phage therapy also may, in the future, improve the management of challenging bacterial infections that are not necessarily multidrug‐resistant.