Citrobacter rodentium is a natural murine intestinal pathogen that shares a core set of virulence factors with the related human pathogens enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC). C. rodentium is now the most widely used small animal model for studying the molecular underpinnings of EPEC and EHEC infections in vivo, including: enterocyte attachment; virulence; colonization resistance; and mucosal immunity. In this review, we discuss type 3 immunity in the context of C. rodentium infection and discuss recent publications that use this model to understand how the innate and adaptive components of immunity intersect to mediate host protection against enteric pathogens and maintain homeostasis with the microbiota.