Bacteriophages (bacterial viruses) and archaeophages (archaeal viruses) target bacteria and archaea, respectively. Bacteriophages control bacterial populations and have potential applications in therapies targeted against antibiotic-resistant bacteria. They infect bacteria, utilizing the host cell's machinery to replicate and then lysing the cell with new phages. Archaeal viruses infect extremophiles and remain survivors in environments as hot as a hot spring. Both viruses have distinct structures and roles in an ecosystem, providing possible applications in biotechnology and medicine. The World Vaccines R&D Conference also supports research to harness these viruses to advance global health.