Within our guts, we house hundreds of different bacterial species collectively known as the microbiota. The microbiota provides many beneficial functions including keeping out harmful bacteria such as disease-causing pathogens or antibiotic resistant strains. I combine theory with experiments to study interactions between bacteria in the gut. I aim to understand both how the microbiota collectively provides resistance to colonization by pathogens, and how we might remove harmful bacterial strains from of the gut if they do colonize.