Current knowledge of deer diseases focuses on a limited number of deer species, including red deer, white-tailed deer, roe deer, fallow deer, and moose (Alces alces), mainly in the northern hemisphere. Although deer have contributed to literature as models providing relevant advances on the role of pathogens in host ecology, population impact and management, there are still important knowledge gaps on the integral role that cervids play in the structure and function of ecosystems and in epidemiological processes, with most pathogens shared with their respective host communities. The variable and complex epidemiological contexts in which deer species are involved, often involving domestic animals and humans, provide interesting scenarios for further research. The effects of changes in deer numbers, population structure, and host interactions on disease transmission and persistence must take into account not only the life history of the parasites but also that of the specific deer host species involved, the environment, the host community (including vectors), and the prevailing management in the populations studied. Deer species are a relevant component of epidemiological interfaces established between wildlife, vectors, domestic animals, and human compartments in the environment, constituting opportunities for horizontal transmission between species and a new space for the evolution, emergence, and maintenance of pathogens, such as prions. Recent anthropogenic effects and the subsequent changes in urban areas, farming, food systems, and natural ecosystems have resulted in increased exposure of human and deer populations to novel pathogens and the establishment of newly shared emergent diseases in deer (e.g., SARS-CoV-2). Among cervid disease risk drivers, those associated with overabundance are noteworthy, which occurs when moderate to high numbers of individuals affect human life or well-being, the fitness of the overabundant species, the density of species with an economic or esthetic value, or cause dysfunctions in the ecosystem. Cervids are among the species most frequently reported as overabundant. Supplemental feeding of deer has long been used to increase density and harvest, and to sustain local populations during periods of natural food shortage, such as severe winters or prolonged summer droughts, or to concentrate or simply observe them, being associated with increased risk of disease transmission. Other risks include the translocation of animals and biosecurity issues. Disease surveillance in deer is key to controlling disease, particularly emerging and emergent transboundary pathogens, in wild and farmed deer. Passive and active surveillance components would ideally be implemented simultaneously in deer species, but the final choice will depend on the assessment of their cost-effectiveness for specific deer hosts, pathogens, geographical and epidemiological contexts, and will require a One Health approach. Risk assessment of deer pathogens of interest to humans and livestock requires the availability of information on the distribution and abundance of wild deer species that may serve as reservoirs for pathogens (integrated monitoring). However, in most cases, we are unaware of the spatial distribution of deer in relation to disease and to host communities, including both wild and domestic. The importance of addressing shared diseases of deer and livestock wherever these two compartments interface is only now being fully recognized. As we learn from past and ongoing challenges associated with disease spillover and spill back, our abilities to quickly and competently address future disease issues in deer continue to improve. A better understanding of the subject requires redirecting scarce animals, public health, wildlife management, or conservation resources. To succeed we advocate for integrating interdisciplinary expertise within and across the natural and social sciences.