In the past, phages were very well studied for horizontal gene transfer and transduction processes, especially for drug-resistant determinants and toxin genes. Now, they and their proteins regain interest for their great antibacterial repertoire, even towards antibiotic-resistant strains, their narrow host range, and their simple manufacturing options. All these features may potentially allow not only to use phages as adjuvant of the antibiotics for the treatment of infections caused by drug-resistant bacteria , but also to modulate pathogenic, commensal, and pathobiont bacteria of the microbiome, impacting host physiology and immune system in a One Health approach.