My main area of interest is the evolution of diversity in pathogens, with particular reference to the infectious disease agents that are responsible for malaria, influenza and bacterial meningitis. I use simple mathematical models to generate new hypotheses regarding the processes that determine the population structure of these pathogens. I work closely with laboratory and field scientists (i) to develop these hypotheses, (ii) to test them, and (iii) to apply them to the control of infectious disease.