The interface between wild bird populations and human populations is expanding, with the emergence of pathogen transmission between birds and humans as one consequence. In this chapter, several case studies of the spillover of avian pathogens into humans, and to a lesser extent human pathogens into birds, are reviewed in the context of the ecological and evolutionary factors that are important for disease emergence. Transmission and disease emergence may be complex, in some cases sculpted by the interaction of multiple parasite species with birds or their vectors. Additionally, avian migration allows opportunities for bird-associated pathogens and vectors to be transported over great distances, sometimes initiating new foci of zoonotic disease emergence. While several management strategies are being used to detect and respond to the emergence of avian zoonoses in birds and people, an increased understanding of the biology and circumstances that support transmission and spillover will further direct such efforts.