Viruses infect all domains of life and have an important role in public health and evolution. We follow basic questions related to the viral biology of infection, with special focus on the envelope proteins of viruses, which they use to enter and exit cells. We address these questions in the human pathogenic hantaviruses and also in archaeal viruses that have membranes. For hantaviruses we have provided molecular insights into the mechanism of fusion between the virus and the cell membrane, and characterized the organization and dynamics of the fusion protein Gc on the viral surface. For the design of vaccine and drug candidates we also focus on protective immune responses against hantavirus, using nonreplicative virus-like particles developed previously by us. Based on our experience with the fusion protein of hantaviruses that infect animals, we have identified the fusion activity of enveloped halophilic archaeal viruses (pleolipoviruses). We expect that future mechanistic information will allow us to unveil how viruses modulate archaeal membranes in this yet poorly explored life domain.