Hans Heesterbeek has a broad research interest on the interface between biology/medicine and mathematics. His focus is on the dynamics of infectious disease, currently in particular on the interaction between (wildlife) ecology and (human disease) epidemiology, with an overall emphasis on the development and use of mathematical tools to generate relevant biological and public health insight, most often in close collaboration with others. One of the methods he contributed to is the way, used worldwide, in which the reproduction number of infectious diseases needs to be defined and calculated for epidemiological models (his PhD-thesis from 1992 was titled: R₀). Recently, he also became interested in using insight and methods from theoretical ecology and infectious disease dynamics to study emerging phenomena in a broad range of complex (social, societal and financial) systems. He has an active interest in the history of science and is currently working on a book on the history of the study of epidemics. In addition to his scientific work, he chairs the Committee for Research Integrity of Utrecht University and the University Medical Center Utrecht.