Phages (bacteriophages) are viruses that infect bacteria. They can be used to treat bacterial infections, i.e., for phage therapy, if antibiotics cannot be used. As pathogenic bacteria are becoming more and more resistant to antibiotics, there is a growing need for alternative treatment methods. The Phage Therapy Research Groups studies phages and their applications from several perspectives and carries out cross-disciplinary collaboration with several research groups in Finland and abroad.