A majority of emerging diseases in humans originates in the animal world. Wild life and farm animals may harbor viruses that can directly or with some adaptations infect humans. Such zoonotic spillovers have been documented for a range of viruses, and constitute a first step in a chain of emergence. Risk of spillover is determined by a complex set of factors, collectively called drivers. Rapid changes in the balance between these factors often precede spillover events. Zoonotic spillover may lead to epidemics or pandemics when the pathogens involved have or acquire the ability to become transmissible between humans. Once that occurs, the efficiency of that process again is determined by a multifactorial process of drivers. Using recent examples, this presentation will focus on the concept of One Health, and the importance of considering the role of animals and environmental changes in emerging disease preparedness and response.