My group works on a variety of topics related to comparative infection and immunity and I will cover aspects of our current work. The first considers interactions between the host and gut microbes, considering how local immunity might stabilise the microbiome. Moving from within host to population levels I will describe the application of a single target parallel sequencing approach to examine the population structure of Campylobacter in commercial chickens. Campylobacter is a significant public health problem and most infections in humans are derived from poultry. One of the key questions is how do the chickens acquire Campylobacter and if we can intervene we could dramatically reduce infection of humans. Our simple method identifies differences in the population structure of Campylobacter in different types of bird, the meat birds (broilers) and their parents. Then we will move from the current day into the past, dealing with parasitic diseases of humans to interrogate the medieval lifestyles. Working alongside archaeologists we have employed parasitological and molecular methods to define a range of aspects of life in Medieval Europe including some unusual dietary practices, changes in the source of infection and epidemiology of past parasite infections.