[Show abstract][Hide abstract] ABSTRACT: Mass antibiotic treatment and facial cleanliness are central to WHO's strategy for the elimination of blindness caused by trachoma. Recent studies have highlighted the heterogeneous response of communities to mass treatment and the complex relation between infection with Chlamydia trachomatis and clinical disease. It is important to be able to explain these findings to predict and maximise the effect of treatment on active trachoma disease and blindness in the community. Here we review the immunobiology of trachoma and provide a simple conceptual model of disease pathogenesis. We show how incorporating this model into a mathematical framework leads to an explanation of the observed community distribution of infection, bacterial load, and disease with age. The predictions of the model and empirical data show some differences that underscore the importance of individual heterogeneity in response to infection. The implications of disease transmission and pathogenesis for trachoma control programmes are discussed.