Global pandemics often begin when a virus jumps from animals to humans, leading to initial cases of infection - sometimes referred to as "patient zero." As the world recovers from COVID-19, understanding how pathogens first spill over into human populations is critical to prevention efforts. The National Academies' Forum on Microbial Threats convened a workshop in January 2025 to examine how ecological, social, and technological factors shape the emergence of new infectious diseases in humans. Speakers addressed gaps in understanding of disease emergence with a focus on the human-animal interface and laboratory biosafety. This Proceedings of a Workshop summarizes the presentations and discussions that took place at the event.