Nearly 60 years have passed since the discovery of Yellow Fever (YF) in East Africa but the disease has remained enigmatic because of unpredictable focal periodicity, lengthy inter-epidemic periods, and a precarious potential for large epidemics. Endemic and/or enzootic transmission has been poorly documented and, as such, typically remains of little value in predicting future outbreaks. The following studies were aimed at clarifying the ecology and epidemiology of YF in East Africa and detailing a number of important interactions associated with the potential emergence and transmission of YF. Three aims were included in this investigation: (1) a study of the distribution of YF among wild monkeys in Kenya, (2) spatiotemporal descriptions of YF vectors along forest interfaces, and (3) an examination of the efficiency of domestic vectors to transmit a local YF virus genotype. Overall, the study indicates that enzootic YF activity has been limited focally and in duration within Kenya, YF vector-human interactions are relatively limited in domestic areas as compared to the forests studied, and the most important vector of epidemic YF is poorly competent. These results have important implications in regard to the emergence and epidemiological outcomes of YF. The approach taken during these studies was to highlight the dynamics of important eco-epidemiological interactions and to provide practical comparative measures. Ultimately, revealing the underlying drivers and dynamics of YF emergence, as evidenced by causal changes, will require quantifiable measure of these rare events or strongly suggestive evidence from inter-epidemic and epidemic comparisons