This issue of Viruses is a living memorial dedicated to Professor Stefan Kunz, who passed away too early in life, at 54. During his scientific career, Stefan made major contributions to the field of virology. He made seminal contributions to our understanding of how mammarenaviruses gain access to and are trafficked within their target cells. This issue of Viruses contains a collection of articles by leading researchers in different areas of virus-host cell interactions and who crossed pathways with Stefan. The topics covered in the issue include novel insights on mammeranavirus cell entry, host innate and adaptive immune responses to infection, recent developments on therapeutics against human pathogenic arenaviruses, as well as mammarenavirus ecology and molecular pathogenesis. The collection of articles is also a reflection of Stefan’s enthusiasm for exploring new ideas and his very collegial attitude reflected by his many collaborations, including the colleagues who have contributed sections to this memorial issue.